MMP does not own the rights to ASL, they have a production license from Hasbro, the owners of ASL.
It does not take long for new players to venture onto GameSquad, Facebook ASL groups, ASL Discord servers and find mentions of new products not on the MMP website.
First, I definitely didn't know that Hasbro owned ASL. I figured MMP, with "publishing" in its name, was probably not the owner and just the publisher, but then if that were the case I'd expect them to "publish" this eBook. Which ultimately I see that they did and now know why it is being sold through Wargame Vault and I bought a copy and yay!
As for the new players will find it thing, well, you may be right. I'm a very new player, but I've been reading ASL message boards and PDFs and trying to play some SK games for about a month now. But I'm a pretty motivated and techno-savvy guy. I'm not sure everyone would find the eRB so easily, but I guess if someone is motivated enough to try out ASL, they will probably find the eRB in very short order.