Same reason as for all those years these old people are holding a grudge for...

It is not Unix philosophy (nothing is these days), it does not solve any problem they ever had (it does), it is no improvement over what we had before (it is) and even makes some broken and moronic things harder (it does), it is insecure (it improves overall system security), and it is one monolithic blob (it is not). Before systemd nothing depended on the init system (true, but then it did nothing useful that made having such a dependency worthwhile), and before systemd we were all free to use other init systems and distributions did not pick one for their users (they always did, offering additional inits only as unsupported iption just likenthey do now).

That's the typical list you get.

Oh, and it was shoved down all our throats by the mighty Lennart himself, backed by several multi billion dollar companies that brided thousands of distribution developers to destroy Linux (it was not).

Funnily enough it is pretty much the same BS we had when that monster of complexity called sysv init was introduced into distributions, replacing a simple script with a forest of symlinks. Of course the community was much smaller then and so we had a loser number of idiots to shout at everybody else.