It has two different UIs (last I checked) which is kind of insane, blue ocean still sucked the last time I used it and the product can’t 100% move away from the old UI (again, last I checked…)
On top of all that it’s not really fun to administer (first-hand experience) where almost every environment will result in plugin hell. I wouldn’t describe the setup process “download a single file and run it” as I look at the documentation, either.
Jenkins can’t give you the “one less tool” advantage that you get with GitHub or Gitlab, either.
Don’t forget that Jenkins’ competition includes free options with mostly high longevity.