I have no idea where you get the idea there is a finite amount of bandwidth available. It is not coal or molybdenum. ISPs are continually being expanded.
The current bandwidth is finite. The future bandwidth is finite. Even if we use all the resources available to us, expanding at the speed of light to capture those resources, it's still finite.
The internet is continually expanding at OSI layer 1. It is a construction project. The bandwidth is growing faster than our ability to fill it.
There are only so many criminals in the world, period. They only have so much bandwidth, either through stealing it or buying it.
Also, I am happy Cloudflare is doing this, they are, at the very least, taking resources away from the criminals that could be attacking others and doing real harm.