I've heard of expansion fetish before; my immediate hypothesis was that it's about mental wiring normally related to pregnancy (the same way foot fetishes are hypothesized to be related to wiring meant for your genitals). I've never heard of someone specifically wanting to be a giant blueberry but it's not hard to guess that once the general pattern of a fetish exists, specific details could be impressed by various conditioning processes.

I can't think of an analogous reaso someone might like chocolate rivers or pneumatic tubes. There probably are people out there who really like little orange people but by a totally different mechanism.

I think it is mostly consumed by men wanting to watch a woman turn into a giant blueberry, not women wanting to turn into a giant blueberry? But I’m not sure, haven’t talked to anyone who was into it.