The modernisation efforts actually do have an impact even for people who are happy with the current look and feel and are not particularly worried about new fancy js and css features
As time passes they allow us quite a few optimisations that can make Discourse faster to load, and generally allow our teams to remove clunky areas from the app
I get that it may be frustrating to some people, but Discourse is a large platform and we strive generally to give a very large audience an excellent experience, this is a big driver for these types of changes