Yeah I honestly find people going for 100% achievements to be absolutely strange to me. Same with New Game+ people. A lot of the time you have to play the game over and over again or do something horribly repetitive to get to 100% and people just do it. There are very few non-strategy games I ever want to play again as much as I enjoyed the first play through.
I feel like the people who don't like "gamifying" github think that that's the similar style of github badges. Someone even mentioned that "you can't 100% life" or some form of that. That is the furthest thing from the point of it in my opinion and experience.
But there are definitely a small portion people who go for that, I'm sure.