I think it just depends on your personality. I have always felt uncomfortable around rats (do not know why). But my sister loves rats, she will just scoop one up and cuddle it.
I feel stressed out with animals that are too "needy". Mice are like the more independant version of rats. Plus, they have a almost fish tank effect with them, as in watching them for hours going about their lives.
Mice do love their owners I think, but they just do not know how to express it. Like they still have their wild instincts of them being prey to pretty much every other animal.
Yes, if you like cuddly pets and love to hug them and give them more of a dog like treatment, then rats are for you. But I do not like to cuddle something for hours or anything like that. So mice work for me.
I think of the rat and mouse difference is close to the differences in dogs and cats.
Maybe it cannot simply be explained why people like what they like. I just know I love mice.