It used to be 26, so you could plan shows covering half a calendar year, then over the years it got cut down more and more. And it was probably not a bad thing because you typically had the same budget but meant you didn't have to do a cheap clip show to pad out the numbers.
That's also why you see a lot of shows with 13 episodes, that seemingly arbitrary number is "half" a traditional season. Even Netflix, despite not traditionally caring too much about seasonal stuff or drip feeding week to week, has a lot of 13 episode seasons.
I guess at some point people wanted even numbers (10) as 13 does feel a bit arbitrary even if there's a reason for it.
Personally for me I'd rather have 10 great quality episodes than 26 episodes where maybe 8 of them are great, 10 are okay and the rest are utter dogshit. The problem is that even (what I consider) great shows like Strange New Worlds, despite only having those 10 episodes per season, still has the odd naff episode.