For one, GitHub and DigitalOcean both had Series A investments led by the same partner at Andreessen Horowitz.

https://www.crunchbase.com/organization/digitalocean/investo...

https://www.crunchbase.com/organization/github/investors

How would they track pull requests? I agree that it would be nice if it wasn't just restricted to github and the kinds of projects most likely to be hosted there, but it does simplify things on their end.

I do wish they had a way to prevent people from gaming it with fake projects just to get a free T-shirt, especially when there still seem to be others that never receive one. It also just goes against the spirit of the event.

Probably because github is a big sponsor and the host of 95% of the OSS work in the past 10 years.