possibly because it was one of the original story ideas of the pixar crew? way back when it was still in post production they released this sappy preview about the original brain trust meeting of pixar stories and how toy story and nemo, and basically all of their best movies were conceived at this one meeting, and then some guy died and they all cried about it.

tl;dr
brainchild of the same guys that made pixars best shit.

or maybe it’s because it’s an adorable goofy robot?
the general public is batshit about adorable goofy robots.
My opinion?
If Skynet had waited a few years afer becoming self aware, it would have realized that the best way to enslave humanity would be by designing cute, affable killing machines, rather than the uncanny valleyfest it chose.