You know, this is a really great point you've made. Thank you for bringing this up.
I had goldfish as a kid, and while I loved them then, today I can't connect with them. Someone mentioned lack of personality, and I think I have to agree. Guppies make me feel the same way. They just move around for the sake of moving around, never seeming to hunt for anything, stalking anything, being picky about foods and so on.
However, I have been noticing that I look at koi longer these days, and I have caught myself having fleeting fantasies of koi ponds...