Even linear television dropped to 16, then further to 12 or even ten. Some serialized sci-fi shows are 6.
One thing to keep in mind, especially with science fiction and fantasy shows is that they take an enormous amount of time and resources to make in UHD. It’s a very unforgiving medium that shows up every tiny flaw in prosthetic makeup, costume construction and set and prop fabrication. The primary shooting takes much, much longer for each episode, 1.5 to 2 times what it did in the 90s.
Yes, they can take short cuts but there is a price for it in terms of quality. As a concrete example, Picard season three decided to go with ambient lighting from the set rather than move and recalibrate lights for every side of every scene (usual practice). It reduced the amount of time needed to shoot each scene, as they could go immediately from one side and scene to another. It did however mean that the final product was darker than many older fans preferred, especially if they didn’t have the newest OLED televisions.
Another thing to keep in mind is that the actors want to be able to work on other projects or have time for their families. Many shows have more established cast members simply because working on Star Trek no longer means locking into a single show for seven years of their careers.
Anson Mount has said publicly and repeatedly that he found doing the 14 episode second of Discovery took too much of his life. He particularly noted that the bridge filming days were very long and arduous, even though he enjoyed being together with the whole main cast for them. It’s known then that he personally wouldn’t go for a longer season.