A handful of improvements came tied to a bunch of new constraints and limitations that were not mandatory to get those improvements. This annoys the people who deal in those less visible areas and got the short end of the stick.

A large chunk of what systemd does could have been implemented without also sprawling it's tentacles and cross-dependencies into everything. Had they rolled out that featureset first and given the rest of the ecosystem some time to evolve in response adoption would have gone much smoother.