If you’re right then piano keyboards are misdesigned for humans. Plausible in my experience.

However, by all reports Chopin's hands were special, and an anatomical key to his success. In At the Piano with Chopin, composer Stephen Heller is cited as extolling how Chopin's slim hands would "suddenly expand and cover a third of the keyboard. It was like the opening of the mouth of a serpent about to swallow a rabbit whole." A student, Adolf Gutmann, also reportedly said Chopin's "whole body was extraordinarily flexible."

Regardless of the size of the keyboard, bigger hands will always cover more keys.

Well, you probably don’t want to make the keys much narrower, since it’s pretty important to be able to hit one specific key with one specific finger.

There are pianos with slimmer keys that may be more suitable for those with small hands (e.g. women). It’s just hard to change a legacy design and push it to the masses. Of course if you’re at the top of the game you can get custom keyboards easily but it’s hard (and expensive) to justify for customisation if you’re just learning the keyboard