Presumably though, they just made the pistons smaller for road use?
How can they have too much power? It's not like they're going to bend a rotor is it? It's just a question of 'can I apply these enough to slow down rapidly, without immediately exceeding tyre grip?'
You can still get larger pads, just not by way of larger total cylinder area. Two smaller cylinders adjacent can provide pressure across a larger pad as not all parts of the pad need support.
That's like asking nodders why they're using a powermeter or why people commuting on carbon rims? I don't know, never having used them, but it's an option that didn't exist previously and might be useful.
Presumably though, they just made the pistons smaller for road use?
How can they have too much power? It's not like they're going to bend a rotor is it? It's just a question of 'can I apply these enough to slow down rapidly, without immediately exceeding tyre grip?'