Those that do likely will already have an actual sales rep and the means to get these restrictions lifted, with a direct line to engineering.
Hetzner certainly markets to a different crowd, which I suspect is why these limits are being put in place ahead of time. It's very difficult to design around noisy neighbor, and will take some battle tested time in production to get right for the "average Joe" style customer who won't engage engineering resources to work with a provider to avoid hot spots and impacting other customers.
My suspicion was also that they're intentionally targeting a different crowd than S3 and focusing on their niche here.
I am not sure about the exact specifications anymore, but they are building dedicated servers for this with custom chassis where each server has a ton of drives and I think they each had 40 GBits networking. These are special servers that are not available to customers directly.
[1]: https://docs.hetzner.com/cloud/technical-details/faq#what-ki...
Is it typical to have such per-bucket limits? This means that you might have to take them into account when deciding on how to organize the data to avoid bottlenecks.