Most splitpushers are AD because AD is better at taking turrets. And most split pushers are less ADCs and the like, and are actually juggernauts. Who you basically can't 1v1. Meaning you need to send two people to handle them, meaning by simply being toplane pushing, you've made it a 4v3 for your team. The only AD split pusher I can think of that isn't a juggernaut is Tryndamere, one of the few AD champions with good waveclear, who is also a massive pain in the ass to kill, and is usually impossible to 1v1.
AP still has the massive advantage in clearing waves, because there's just so few AD champions who are actually good at it. There's not a single mage who doesn't have an ability for waveclear, while at least 70% of the AD roster has no waveclear outside of Shiv (which does magic damage), or just attacking really fast (which isn't waveclear, no matter how fast you're hitting).