It does seem logical that if transport and return to and from Isekais were a real thing, and somewhat common, that the authorities would catch on eventually.
Actually, this has been in the background for a number of chapters.
The "information wants to be free!" part of me dislikes the idea that this is something that would be kept from the general public.
The more sensible part of me says, "Hell, yeah, keep it under wraps, just think of the types who'd set out to figure out how to transfer and return with magic powers!", and also, like, it's Men in Black, ya dig?