Hetzner offers a 99.9% uptime guarantee only on their network. AWS has SLAs for every product offering - EC2 for example starts paying out credits if they fall below 99.99% uptime.
If you're a user of various managed cloud products, these will cost quite a bit to replicate on Hetzner and you'll be spending money on personnel to build these out and maintain them instead of just paying for the cloud product on AWS/GCP/Azure.
You need postgres? Use crunchydata postgres operator or cloudnativepg. Need multiple regions? setup wireguard.
IT's more work, but might not be a lot of work.
Also, I've seen a lot of concern over blocked IPs, especially for lower-cost hosts. Is that an issue with Hetzner?
Still, Hetzner cloud is pretty good option, and there's more support coming on building on Hetzner.
https://www.ubicloud.com/ (from founders of citus) is mainly/currently targeting hetzner, for example.