I'd doubt there's huge money being made by Amazon, but if they give a profit cut to one or two companies that make products AWS offer as a hosted service, then a bunch more will probably also start changing their licensing to match. Putting resources into building an alternative that discourages this is probably not as much as it might appear (there are already plenty of developers at Amazon, and it's unlikely they're all working on other things that need to take priority), so it may be a good investment.

My company uses it and the bill isn't small. I can imagine that other thousands of customers provide substantial money as well.

Amazon's thing is the network effect, not margins on a particular feature.