You're totally right about software being more about people than about code. That being said, I think maybe you're underestimating just how many issues ESLint receives and how willing people are to volunteer time to the project. They've received almost 2500 issues and have essentially 5 active developers.
Yes, you're one hundred percent correct that issues are the problem here. That's a lot of issues for five people. Period. You're being a little lenient on GitHub's behalf by not weighting how poorly it does issue tracking which expounds their problem a great deal.
They're not "typical dumb engineers". They mention nowhere that they'll somehow end up with less bugs if they leave GitHub. But they believe they'll be able to more accurately assess issues and turn them around faster by using a different platform--which if you're familiar with the alternatives, it isn't the completely facetious assumption you cut it out to be.
Sorry if that comes off aggressive. Not intended. You make great points. Just wanted to reiterate that GitHub has some blame here...