Aside from what others have said, it does matter because few people apply the proper amount. If you're applying only 1/3 the "proper" amount of a 60 SPF product you still at least get 20 SPF of protection as it scales rather linearly.

And as someone paler than most makeup brands go, for many of us it absolutely does make a difference even when using the proper amount.

I ride or die LRP uvmune 400, few protect as well as it does.