The Comic Board

I'm curious if DC has a lore reason beyond the Infinite Frontier that explains these different mediums that bleed over into other multiverses within I guess this mega-multiverse...

That is essentially what I think is intended, somewhat. I personally feel like, when they create tie-in media, it is supposed to be set in the exact same reality as the other material. To be fair though, we do see this happen a bit. Earth-616's X-Men went to the Star Trek Universe, but Star Trek remains undesignated. (Obviously Marvel is different, but there's cosmic overlap)

I feel like certain realities just appear to exist in multiple multiverses at once, probably as some overlap. Similar to how, say, the Amalgam Universe exists in Marvel's Multiverse, but also multiple iterations of DC's Multiverse, and yet, we don't argue that there's three Amalgam Universes.