You're theoretically more in control of the data, which may be a legal requirement in certain jurisdictions and/or industries.
https://www.zdnet.com/article/whats-actually-in-australias-e...
Legally many of our clients require that their data, all of it, secret or not, reside within the EU.
Currently cloud is not so hot, due to Schrems II. During the last six months we migrate a number of customers on-prem, and only one is building out their stuff in AWS.
There's a fair few reasons other than this, it's not unthinkable to host servers yourself if you already have other servers on-prem anyway.