I wouldn't call it legacy as that implies something people inherited but didn't want. The common sentiment among kernel developers has always seemed to be that device trees are nicer to work with than the complicated PC abstractions, and that sentiment remains today. And IIRC Linux didn't always have device trees; it was an approach that came later as it was ported beyond x86, Alpha, and SPARC, and was welcomed.
I'm not a kernel developer, but it seems to be one of those things that's great when you're adding support for a particular device on a particular platform, but becomes a giant PITA in the aggregate for the downstream ecosystem. It's a mismatch of incentives and preferences.