There is a reason people would complain that "every week is the same story!". That's because the constraints of the medium meant that you had to keep deviations to a minimum.
Black Mirror is akin to making a movie for every episode. Every episode has different actors, which means they need to be cast. They have different locations, which means they need to be scouted or built. They have different characters which means a lot more work for writing because every character needs a backstory. Basically they have to start fresh for every episode.
Something like Stranger Things is sort of 1/2 way between -- they have their characters and actors, but they have a lot of locations, and the story varies wildly from episode to episode. Each season is like making a really long movie.
And that's just the production side of it.
From the business side it doesn't make a lot of sense either. The whole point is to provide fresh content for users. If you can provide a new show every month, that's a lot more compelling than a new episode of the same show.
If they could invest in only the hits, they would.
If they could reliably improve their customers' happiness with their service, at minimal cost, they would.
If they could cut down on the expense of actors and sets and writers, they would.
But in more seriousness, I'm sure they are trying to optimize for producing the least amount of content in order to retain existing users.
At an episode a week, you run out of plot way faster, and your humans are basically signing on to have no other work.
It's also incredibly expensive, something Netflix some how disregarded when they decided to make/own most their own content. Thus the excess of low production quality shows
Build an evergreen catalogue. Nobody is watching old sitcoms, but new people watch Lost everyday even though that also got badly affected by quantity requirements due to hype of the day.
But if I understand Black Mirror correctly, it's an anthology without a shared world/characters. There'd be diminishing returns much sooner with additional episodes. There's only so much to say about that theme. And we're living it every week anyway.
The standard strategy is to fund spinoffs of popular franchises. Marvel is a good example of this taken to the extreme, where there literally is a constant content stream.