I think the biggest thing is that the minimum extra spend if you want in house managed infra is basically the salary of a full time sysadmin + hardware costs.

You can pay for a lot of cloud resources for that much, even when the cloud resources are massively overpriced compared to what you could manage if you had more scale.

The only other alternative is finding someone who's good enough at it to make that full time sysadmin job just a small part of their "actual" job responsibilities, but that person is pretty hard to find.