Sometimes you want to avoid competitors, or foreign governments, or intelligence agencies from accessing your data. Sometimes you want to avoid any kind of tracking or metadata analysis. Sometimes you want to avoid external points of failure.

Often it is cost - even including wages, AWS or GCP are a factor 10 to 100 more expensive than what you can run on rented dedicated systems from a local hoster, or by colocating. Even your own datacenter can be cheaper, and end up with identical uptime.

And then there's a question of trust. A simple question: Would you trust a Chinese SaaS company to securely store all your customer's data, and run all your services? Would you trust a Romanian one? Why would I trust an American one?