Purpose of gate driver in Class D amplifier

Can somebody explain to me why we need MOSFET gate driver in class D amplifier like in the picture below(common class D schematics)?
What I don’t understand is if we for example have 9V rails, then the comparator(LM311 for example) would output PWM waveform with 9V level. If we then use MOSFET doesn’t it just becomes equivalent to wire? So, wouldn’t it be the same if we just connect it neglecting MOSFET driver?
I understand the concept of MOSFET amplification if we have weak signals, but for me we just converting 9V pwm to the same 9V pwm here. I was trying to see how the current changes if we place MOSFET, but also don’t see the difference…
One reason I can think of is that comparator has high output resistance which limits the current, I wonder if that is true, but still if we connect 8ohm load to it shouldn’t matter so much.