A more cynical point of view: Product positioning.
- A theatrical release is considered a "higher league" in mass consciousness (eg: Oscars being more prestigious than Golden Globes).
- Wide screen format is associated with theatrical release.
Therefore many shows, both films and series, which are meant solely for streaming/TV are filmed in wide format to give an impression of "cinematic experience". This is done to invoke connotations to a "more premium" product. While technically it seems counterproductive (given that amount of ultrawide consumer screens is negligible) but psychologically it makes many viewers feel better. Especially on paid streaming services - spending money on subscription feels more justifiable if you get in return a theatrical film (which "costs ticket money") rather than a TV production (because "TV is free").
Similar thing keeps filming in 24fps alive. There is no technical reason to stick to choppy movement, but we (the viewers) are simply used to feeling that choppy = good and smooth = soap opera. Even being aware of the conditioning doesn't change the fact that watching 60fps makes you think "it feels cheap".
Of course, filmmakers tend to invent lots of excuses to explain either marketing department decisions or their own (often subconscious) ones. But it's quite a coincidence we rarely hear artistic arguments proposing filming in uncommon formats. It's always "TV screen vs cinema screen". The reasoning hasn't changed since when TV was 4:3 and cinema was about where 16:9 TV is now :)