Many of us starting using Linux before systemd was a thing, and you get used to what you use, so when something new appears that are trying (well, in this case "tried and succeeded at") to replace a bunch of stuff, there is a natural push-back against it.

I think systemd also took a relatively non-unixy approach, where it's a big stack to adopt, rather than individual programs that work together well. Typically, we prefer the latter instead of the former, so some pushback is because of that too.