Its hard to pinpoint how any kind of fetish forms. Usually something from somebodys younger years before they were a teenager "triggers" something in their head.
Alot of guys like fake tits because in part its the woman taking charge over nature and giving herself bigger boobs. Powerful headstrong women. Breast expansion fags also usually get into liking girls with implants because its one an extremely few forms of real life breast expansion. Sometimes its just guys with a caveman brain thats goes "Hmmm. If booby good, then bigger booby be ever gooder!". Some guys just like the aesthetic for any number of reasons. Theres also a suprising number of women with fake boob fetishes and get their own.
Also>They look so unnatural and wrong
That really only happens with really big implants, or girls with very low body fat. Girls with some thicc'ness are able to make implants work way better and actually look natural. Especially if they stay with a more "realistic" sized implant.
I say all this because Im also an implant fag. But I also love huge naturals too. And flat chests too. I like all boobs.