I think you're missing the part where a lottt of the people with sex dolls are not just using it to physically stimulate themselves, but are often pretending its their actual girlfriend(/boyfriend) (at least most of the owners shameless enough to post about their dolls online).
That's the aspect a lot of people find the most creepy, that theres a 5'0 fake woman with dead eyes just chilling in their house 24/7 being roleplayed with thats also being pumped full of jizz.
Its like porn just playing 24/7 on someones living room tv without being able to turn it off. And since a lot of these dolls look creepy af, the porn in question looks like potentially pedophilic necrophilia.
I remember a while ago on the farms I saw a series of posts about a guy who made one of his sex dolls 'give birth' and made HIS MOM deliver the 'baby'. That kinda person is who i imagine when i hear about sex dolls, because if there are decently normal people using dolls the same way theyd use a fleshlight or whatever they arent the main ones posting and representing themselves...
I also think a big part of the normalisation of dildos vs fleshlights is that a million porn vids with them are made every day, while fleshlights/etc not so much. A product being represented mainly by people who arent repulsive in mainstream media goes a long way.
If the main face of dildos was fat unhygienic nonbinaries rather than regular whores, theyd probably be more controversial.