Because imo... that is the answer. We have seen so many stupid closed ecosystems of home automation stuff come and go, I dunno why you'd mess with anything else at this point. In fact I just got another email reminder that Google is turning off the old Works with Nest stack. Remember Nest? Yeah...
They provide a pretty locked down image that also loads a ton of plugins in dockers. It's nice and well designed. And you don't have to expose it to the internet if you don't have to.
The installation described is legacy and only supported for historical purposes.
I agree that Hue has totally gone down the toilet but the criticism of Home Assistant isn't justified. And if you go for the Ikea one as recommended in the article, it's just going to be a matter of time until their shareholders will want to see those sweet recurring bucks too. You need a truly open ecosystem to avoid that from happening.