Television

It depends on the series, there's not a single formula good for all. If you want a dramatic "8 hours long movie" like The Last of Us, you cannot get a 24 episode season, because it would be boring/inconclusive, and the years between season is neede because these series are hard to make and take a long time. You can't have the cake and eat it too, it's either high quality series or one season every year (also see Fargo for an exmaple of this, one of the series I enjoyed the most and they take their good time to delived it).

If you like want less action drama and prefer extensive character and world building (see Star Trek), it's very difficult to do so in 12 episodes, so 24 was used to sprinkle small details in a broader picture, and while the "monster of the week" trope is sometimes silly (also see early Star Trek) it sometimes make sense in the universe of the show (like Star Trek Voyager meeting a different species ebery week because they are literally travelling through the galaxy, or crime shows where you a literally going through a detective's life one case at a time, while exploring their character and culture). With a lot of episodes you also have the advantage of being able to explore a ton of different topics and take your time to properly do it, more than an 8 hour movie can do. Also these types of series usually are less expensive to make so it's easier to spit out 24 episodes seasons every year (altough it's equally easy to drop in quality). They can also feel more "down to earth" insteaf of bombastic, if you appreciate this (like I do) they can be more enjoyable than the protagonist trying to save the world every season.