I saw Black Mirror: Bandersnatch (2018) and got a dead end by choosing the option where the protagonist destroys his computer when his "finished" code turns up buggy. But instead of continuing the story forward, the show kept repeating that scene and asked me to make a different choice where he just hits the desk, thus indicating a dead end.

The protagonist is already frustrated to the breaking point at this point, as his demo was a failure with his boss, so I felt the natural reaction would be that he would destroy his computer; but the show said otherwise.

Strictly from a screenplay point of view, why were there dead ends like this in the story? Why didn't they lead to one of the filmed endings? Keeping dead ends in this novel approach to storytelling seems very odd.

PS: The answer to another question indicates there are more dead ends too

Another reason it may be done this way to motif the video game concept. In some games, you don't always just die, as much as you may have some "players" left and can return to previous checkpoint. (ie: the difference between loosing something vs losing everything/the whole game)

Checkpoints are locations in a video game where a player character
respawns after death. Characters generally respawn at the last
checkpoint that they have reached.**A respawn is most often due to the
death of the in-game character, but it can also be caused by the
failure to meet an objective required to advance in the game.
Checkpoints might be temporary, as they stop working when the
character loses all of its lives. Most modern games, however, save the
game to memory at these points, known as auto-saving.

Checkpoints might be visible or invisible to the player. Visible
checkpoints might give a player a sense of security when activated,
but in turn sacrifice some immersion, as checkpoints are intrinsically
"gamey" and might even need an explanation of how they work. Invisible
checkpoints do not break immersion, but make players unsure of where
they will respawn. Usually, if a player does get a game over, then
there progress will be lost, and the player would lose all of their
checkpoints.

"...why were there dead ends like this in the story? Why didn't they lead to one of the filmed endings? Keeping dead ends in this novel approach to storytelling seems very odd."

But also to go with Johnny Bones' great answer, the notion of different kind of endings also does not only point out that we don't have full control and that there are still limitations, but it also gives us a contrast to consider what an ending really is, which the creators behind Bandersantch seem to want us to contemplate, as they themselves have...

Even Netflix says that while there are five “main” endings, there are
multiple variants on each that they are daring viewers to uncover. And
Brooker and Jones are clear as to not “prescribe” one ending over the
others, especially because they couldn’t agree on what exactly defines
one.

“There were quite heated debates about what constitutes an 'ending,'”
says Brooker. “There’s a school of thought that says any time it stops
and you go back, that’s an ending. In Bandersnatch, there are endings
that are really abrupt that are still endings, in my mind.”

Besides, Jones points out: “In a world of parallel realities, maybe
there is no ending?”

The show is based on the "Choose Your Own Adventure" series of books, and in fact the publisher of said books has sued Netflix over this series.

The point is, in the "Choose Your Own Adventure" books, your character could die, thus making for a shorter story. In the TV show, it must run a specific length, thus the dead end forces you to choose an alternate course of action to progress the story along.

Keep in mind, they're on a budget. It's easier (and less expensive) to force you to make an alternate choice than to actually script and film every possible outcome.

Of course, the simple fact is that you don't really have a choice. ;o)

Not all those ends are as dead as they look

Some of those dead ends lead to new content which helps establish the feeling something strange is going on, that time isn't strictly linear in this story, and that something else is somehow in control.

For example, when Stefan first arrives at Tuckersoft, Colin's code encounters a bug (what was it again? A buffer overflow caused by some kind of sprite?). From there, everyone goes into Mohan's office and Stefan presents Bandersnatch (game). Neither Colin nor Mohan have heard of the book.

Then, Mohan asks if you want to work with Tuckersoft. If you select "Yes", you immediately run into an ending where Stefan releases the game, it's buggy and half-finished, and a terrible game. Then you encounter what you've described as a dead end. The movie prompts you to go back to your last decision and try again.

BUT! This "second" time Stefan arrives at Tuckersoft, things go a little differently. This time, when Colin's game breaks, Stefan cuts Colin off and explains the bug he runs into. Further, inside Mohan's office, both Colin and Mohan know all about Bandersnatch (book). This shows the viewer that although you're repeating the major events, your choices have a lasting effect on the Bandersnatch (tv show) world. Colin even breaks the fourth wall on this during his acid trip (a few other places as well), and is so confident of it he's happy to jump off a building to demonstrate.

Further, some future options change based on the decisions you've made in the past. In the answer you linked to, you'll see you can pick up some "qualities" along the way, which affect the options you have. It's possible to encounter an apparent dead end, only to realize you unlocked another path along the way. For example, you can go back in time and find Stefan's rabbit as a child, but only if you've talked about Stefan's mom.

Then, of course, from a game perspective (because Bandersnatch lands somewhere between game and TV), every choice can't be equally as significant or correct. That's bad game design. You can see a couple of places where they thought about this: the non-consequential choices at the beginning show the viewer how choices work; selecting "yes" at Tuckersoft makes sense, so most viewers are immediately shown how they can go back and change a choice (and how that affects the story). So dead ends are a little necessary if you want the viewer to feel like they need to put effort into their decisions.