Only because we thought such a robot would be like a AGI servant, not just a single-purpose device like a roomba that can just bounce around the floor.
So, it's not like we've changed our definition of AI (and even less so, AGI). What we did change is what a robot house-cleaner product is (less "C3PO with a broom", and more "single-purpose vacuum cleaner with heuristics to bounce around").
Even for chess playing, when people in the past thought a chess playing machine that would be able to defeat the human champion would have AGI, they did so not because they thought playing chess is enough to signify AGI, but because they thought AGI was necessary to do so.
If someone had explained to them back then that such a future machine would be able to play expert-level chess by mere number crunching of a huge list of moves, and that it wouldn't imply any other thinking facultu, they wouldn't consider that to be AGI.
>At this point the definition of AI is practically "Something computers can't do yet", though I'm partial to its corollary "Any sufficiently misunderstood algorithm is AI.
The practical definition of AI (as used colloqualy, in the market etc) for products is basically "any smart-looking algorithm, with heuristics to do something slightly complex".
It's just that the term is overloaded, and we sometimes say AI when we mean AGI.