[tamimio]

Not just the cost, but you are not under the mercy of someone else ToS and you are in a full control of your system, the only justification against on-premises are either you don’t have the proper infrastructure like a reliable internet access or the capital cost upfront.

[shitlord]

You are always at the mercy of someone else's ToS, even if you own your hardware.

[dangus]

This works both ways, though. If something goes wrong with an AWS managed service, they are the responsible party. You have someone to sue.