The Piano's Got Bigger, Right?

There are theories as to why the piano's got bigger. People getting larger was one theory that came up. Women also got larger, but we're still not as large as te keyboard is. And then finally, i think all of this coincided with industrialization. So at some point during those overlapping things, it got fixed in as a size. Why can't we change it now when we know smaller keys can work on pianos?