Here's my hypothesis: HB could've added all of the missing features (including ALL of the licenses) if they wanted to, but they tried to keep the budget to an absolute minimum. They are assuring themselves of a profit no matter what. I think they probably have small features like replays and online ready for the next installment, but they'll only add it on when the next game releases, that way we'll all be very happy with how the game has improved but the core gameplay, I'm sure of it, will stay the same. Rugby 15 is basically just a quick cash-in to showcase the gameplay of future, much improved, rugby games.
Rugby 15 is not the full game HB Studios are developing unfortunately, it's probably a game that has gone halfway through development and is now being sold to help fund for further development of the full game.
I'm pretty sure this is their thought process.
With that said, I'm happy to support it since the gameplay looks like a lot of fun.