DevTools is a big one.

Not OP, but as someone who has used Spring quite extensively (6+ yrs) in the past and using Quarkus for all project these days, DX is much better with Quarkus.

Hot reloading (to the extend that change-save-refresh would feel like working with a python/ruby projects), shallow stack traces, less 'magic', , excellent documentation, plethora of modules, less memory footprint, milliseconds start/restart (owing to compile time wiring), first class container support, dev tools, always running tests are few that makes DX with Quarkus amazing.