Teaching a whole bunch of developers some cloud basics and having a few cloud people around is relatively cheap for quite a while. Plus, having test/staging/prod on similar configurations will help catch mistakes earlier. None of that "localstack runs just fine but it turns out Amazon SES isn't available in region antartica-east-1". Then, eventually, you pay a couple people's wages extra in cloud bills, and leaving the cloud becomes profitable.

Cloud isn't worth it until suddenly it is because you can't deploy your own servers fast enough, and then it's worth it until it exceeds the price of a solid infrastructure team and hardware. There's a curve to how much you're saving by throwing everything in the cloud.