They offer self-hosted models for big corporate customers. I would also expect those serious about the security of their data to use that option.
So you would never get the usage of those customers
If you are a company based in Europe it is silly to give your data security and privacy to a company based in Europe.
If you are in Iran, you don't want to give your data to your government.
If you are in France, you don't want to give your data to your government.
etc
If you are in France, and you host your e-mails in a datacenter in Hong-Kong, well good luck for the authorities to get it.
If you host it in "secure France", on the paper you will have more privacy and laws behind you, but in reality you are jumping into the mouth of the shark.
This is why governments are promoting: "yes yes, host here don't worry, we will protect you"
If you are a company based in Europe it is silly to give your data security and privacy to a company based in Europe.
If you are in Iran, you don't want to give your data to your government.
If you are in France, you don't want to give your data to your government.
etc
If you are in France, and you host your e-mails in a datacenter in Hong-Kong, well good luck for the authorities to get it.
If you host it in "secure France", on the paper you will have more privacy and laws behind you, but in reality you are jumping into the mouth of the shark.
This is why governments are promoting: "yes yes, host here don't worry, we will protect you"