It's a pretty non trivial problem to build and maintain infrastructure and customer relationships at that scale, yes, including the myriad of services they provide other than just "compute slices".
Their revenue is like $670bln. If you come up with an innovation that increases that by 0.01%, say by better optimizing prices or targeting adds, you've added $60m of revenue. If you pay a star engineer $1m per year and they have even a reasonable chance of an improvement on this scale, or a similar reduction in costs, then you have a super profitable deal.
I don’t think anyone in senior management actually thinks like that. The company works on a plan (for better or worse), and the resources needed to fulfill it.
There are teams for maintaining massive services where you can build promo packets with a couple <1% cost reduction PRs. I've worked on a non Amazon but similar team where half our M2's org charter was explicitly cost reduction with KPIs of x dollars saved (measured using CPU/memory/etc that we had formulas to convert to infra dollar equivalents).