Multi-region is difficult and expensive, and a lot of projects aren't that important. Most of our infrastructure just isn't that vital; we'd rather take the occasional outage than spend the time and money implementing the sort of active-active multi-region infrastructure that a "correct" implementation would use. We took the recent 8 hour us-east-1 outage on the nose and have not reconsidered this plan. It was a calculated risk that we still believe we're on the right side of. Multi-AZ but single-region is a reasonable balance of cost, difficulty, and reliability for us.