I think a lot of Apple engineers would love to have more time to be able to fix bugs but for the most part they're all stretched pretty thin.

Prioritizing fixing old bugs over developing new features isn't a call an IC can really make so I'd kinda argue that the issue is either "overstaffed with designers+execs who spend engineer time on UI changes" or "understaffed with engineers in general" and not an issue with the mindset of the current engineers.

Or it's too annoying to triage, find (If app store search is anything to judge by) and replicate bugs because the tooling is too annoying or not collecting the right information if people submit bugs. If that's the case then even if you would in theory have the resources to work on bugs it will not be very efficient.