This is not as trivial as you make it sound. You would need to know the amount of functions you want to have provisioned at all times, if you need more, cold starts will occur. In addition this creates base costs, which would not exist otherwise.
I would argue that if you needed n number of functions, where n is unknown, or n cannot be set to a reasonable number that can handle traffic, and cold starts are unacceptable, you would be using the wrong bit of infrastructure.
