To over-simplify, it's about conflicting philosophical alignment:
- systemd: integration and features at the cost of complexity and scope
- traditional: simplicity and composability at the cost of boot speed and convenience
systemd conflicts against the more traditional unix philosophies as well as minimalism.
systemd also replaces some pre-existing services with its own reimplementations that are worse. The systemd developers aren't e.g. DNS or NTP experts, but they act like it and the results reflect all that.