It could be if our workload was relatively stable and there were spare engineering cycles to undertake a migration and all that this entailed. Neither of these is the case.

Much of what allowed us to implement these savings quickly with a small team was the flexibility afforded by cloud infrastructure. Poor decisions are easy to reverse, but in a bare metal world you better be damn sure what you're doing, which slows down the decision-making process and seriously complicates experimentation. The number of people who know how to build out datacenters at the scale of thousands of machines is vanishingly small.

We'd also need to replace IaaS services like ECS, ELB, ElastiCache, RDS, and DynamoDB. There are certainly off-the-shelf replacements, but we'd need to build-out the expertise within our teams to operate these systems. We're talking roughly a dozen or so engineers working full time for many, many months to get these systems in place from scratch, on top of the even larger effort to design and build out datacenters. I'd much rather plow those cycles into efforts like expanding to multiple regions and improving reliability of internal services. That's a much better return on investment for our customers.

Right now we're in the sweet spot for the cloud. We're way too big to run on trivial amounts of hardware, growing at a rate that makes it difficult to stay ahead of demand in a datacenter-centric world, and too small to justify investing in a scalable hardware build-out.