I think terminology here is a big issue: semi-coop is simply a wrong way to define a game, and after a decade or playing hundreds of games with the widest possible audience I honestly can't remember anyone ever using it. I know it's used on BGG, but to me it sounds really weird.
A game is either cooperative or competitive. In a coop you must collaborate to win, in a competitive not. There are some variant to both (team vs team, traitors, alliances and diplomacy) but the bottom line is the same: a game is coop or it's not.
Why this matters? Because in a cooperative game the only way to win is to cooperate. As simple as that, that's everyone's top priority, be it playing against the game or another team, if you don't cooperate you lose.
Then, once the dust has settled down, once everyone is happy because the game is won, many games have ways to declare who was the best player; that player is now the winner among the players, but every one won anyway.
That's why the idea of semi cooperative is odd. There is no semi, you either cooperate to win or you lose.
Arcanist Lupus already mentioned the social aspect. It's something that come up every once in a while on RPG.se too, but every time I expose my theory I get downvoted brutally, so let me try here too :-D
It's really simple: no one has been kidnapped by the Nazists, put on a train, chained in a cold wooden shack and forced to play a game with other people. We are all happily living in a very nice environment where no one has a gun to our head to force us to play anything nor to force us to play with people that we don't like.
In my current city I manage a group of 850 players. We meet and play every Wednesday for 5-6 hours in a row: we get to know each others, we interact a lot, we form friendships. And we form ideas of each others play style. So on Wednesday, if someone invites me to a table, I can still say no if I don't like their gaming style an then join another table. Or I can sit there all evening drinking a beer enjoying conversations, and then invite the people I like at my place to play something else.
And maybe I'll invite some specific people to play Terra Mystica because I want some very competitive players, but I'll not invite some of them to play Mage Knight because last time we tried it's been a disaster.
The game rules do not need to babysit me or solve any issue: I am an adult and I can choose which people I like to play which game with. And when. And for how long. Etc.