> The project is open source, you can fix it, send a pull request, and the whole community will benefit. I wonder if it would have been better if the Yarn developers would had done the same.

Yeah right. It's not as easy as "hey here's a big PR that overhauls the install algorithm and caching!" and npm will be like "ok merged". A PR (or series of PRs) like these would stall for months or even longer (just check out the amount of open PRs and issues in the npm repo).