It's so weird that Pluribus has 9 episodes in a season. I know there's no actual reason for them to stick to standard show orders when they're on a premium streaming service but it still seems weird for them to buck the trend, where most streaming networks would do 10.

Where did the conventions of typical season lengths come from, anyway? I know some of them were due to syndication requirements and calendar-based scheduling blocks but in this day and age why do most shows still stick to them?