This must be the most possible reason why betpanda create a new link (mirror) for Japanese gamblers, maybe betpanda see that there are many potential gamblers from Japan while if gambling is banned in Japan means that most Japanese gamblers are unable to access gambling sites.
It is basically similar to what is done by Stake and Bitsler with their US version which is to serve US gamblers, of course it is just speculation but I think there is no other reason why betpanda need to create specific link to Japan.
Most of the gambling sites have mirror sites but as far as I know these are for the purpose of load balancing. For example, if there were no mirror sites, all the load would be on the same site but since the load can be divided by mirroring, it helps the gambling site to operate more efficiently.
Also if for some reason, one domain name / site is down, the other ones are readily available. But this is done by the old trusted sites or the ones that have established their business. You won't find such features with newly created online crypto casino.