Why didn't Pita compromise?
Obviously I don't know, but I have an idea.
If he had, he likely still wouldn't become PM, and even if he did, it would be a hollow win to have betrayed his voters, just another corrupt politician who doesn't stick to any core principles.
But going down "pure" as he's a young man, perhaps he's playing the long game.
A martyr as it were for Thai democracy. No guarantee such a gamble will even bear fruit, but at least he can look himself in the mirror without barfing.