To hazard a guess, I bet it's a license agreement issue. Originally, Tennogen was available only through Steam, but then they gave it to PS4+XBOX. It took time to get old stuff moved over to consoles because the original agreements needed to be renegotiated. Newer Tennogen was able to come out sooner with an already-revised agreement. In this scenario, the Switch version has launched, and I think the agreement needed to be changed again to account for this. Round 15 would've already been under a new revision, and wouldn't require changes.