In many ways this makes sense. It's more interesting to see someone's hard-honed skill at work than to simply watch genetic advantage play out. Gulliver could win the Lilliput marathon without breaking into a run - but that wouldn't make him an athlete. I feel a bit like that when watching basketball: there must be many keen and talented players who just happen to be under six feet tall. Couldn't they have a league of their own, just as the lighter boxers get their own weight?
But why stop there? Isn't talent itself something of a genetic lottery? Admittedly, even if we wanted to it would be hard in practice to handicap talent in games, because it's difficult to say where in-born talent ends and those other skills for which we might feel justified in giving people personal credit (hard work, practice, determination) begin. We may also want to handicap people for other unearned advantages, such as having access to good facilities, the best coaches, etc. How are these things fundamentally different (apart from not being against the rules) from other performance-enhancing aids?
Of course, people don't want to see hard work alone rewarded. Hard work inspires admiration, but talent inspires awe - and that's what pulls people in. There's something contradictory in all these efforts at ensuring a level playing field in some parts of the pitch and cheering its bumpiness in others. But then, I'm not really a sports person.