Why is 3/2 the majority vote wins in OFA but no for surrendering?

Prbably because a game can be turned around and is a bigger deal than an OFA vote...

Surrender vote is set up to be a 2/3 vote rather than a 50%+1 kind of deal.

Which makes sense, because really - surrendering is a pretty big deal with extremely negligible befits in doing so.

Also, it's important to point out each game has 10 players rather than just 5, so a 3 person vote flat out ending a game is only 30% of the total players.

And finally - 2/3 allows some wiggle-room for a miss-click and prevents duo-queues from abusing the surrender vote with only needing 1 extra vote.

Because life is very unfair. And with every 2-3 people on a team with some sense, there will be 1-2 people who are idiots.