It doesn't make sense to limit HEAD requests though as all S3 implementations store this metadata inside a KV database which is _built_ to handle much more than 750 reads per second.
Edit: There's an ongoing discussion here https://forum.hetzner.com/index.php?thread/31569-will-per-bu...
I do not know if this is a hard limit or if some kind of burst is available for spikes. Constant limit per bucket without considering bucket size makes no sense. At least charge for operations as well.
Maybe they just can't scale quickly enough or maybe they consider object storage just for backup/archiving purposes.