There's no big company bankrolling it (well there kinda is since ubiquiti hired the creator, but not to the same extent something like Chromium is just google), there are a HUGE number of committers, and the structure encourages people to maintain and improve their own contributions via 3rd party packages.
There's no fighting, there's not much gatekeeping, it's not overly complicated, and they are EXTREMELY welcoming to new contributions, no matter how "unique" the use case is (look at some of the integrations! There's integrations for local bus schedule systems!). And on top of that, there's world-class documentation! That's rare enough in paid products, but to see it from a project like this, and the fact that it's almost always up to date is simply amazing.
They held my hand through creating 2 new integrations, and I haven't developed in python for almost 10 years, and they were extremely helpful, responsive, and at the end of the day the product got better for everyone.
I really don't have enough good things to say about Home Assistant.