What they "need" is irrelevant. They deserve every penny.
If valve never existed, the best case companies would make way less than half as much on PC gaming, and a meaningful proportion would literally make nothing because distributing software for revenue is extremely difficult for a normal person or small team to do. Anyone paying 30% is getting a bargain, because distributing the same volume by themselves would cost more than that in labor and other costs.
The entire PC gaming market exists because Valve created it.