It takes 40 votes to prevent the other party from putting something in a bill that you're willing to do a government shutdown to prevent. That's probably a good thing. Consider what would be happening right now, when the Republicans have >50 but not >60, if that meant they could actually do whatever they want.

And the difference between 49 and 51 is still pretty damn important because "majority" has a lot of procedural consequences that are not irrelevant.