Because they would be violating the laws of another country. The fastest way to prevent this is to prevent access from France. The same way it is being done with the UK.
A foreign country can only threaten you if you depend on revenue from this country, or plan to go there. In theory one can even pull of a project like GrapheneOS completely anonymously (assuming you're in a proper free speech jurisdiction that won't rat you out), so people behind it can still travel freely.
French citizens deserve privacy no less than anyone else.
They have no obligation to do otherwise. - ~~~~