I mean, it's pretty clear that Awakening blew up mostly due to a) Nintendo of America actually advertising it, whereas the most advertising I can remember of any previous game was the original GBA FE having some screenshots in booklets of other GBA games together with other upcoming RPGs and Radiant Dawn getting one short E3 trailer; and b) being more newcomer-friendly, whereas the older games had built up this reputation of being much harder and unforgiving than they actually were (not helped by reviewers, I remember this one review for RD where the person specifically started by saying they hated strategy RPGs and were bad at them, but counted its difficulty as a negative).
3H is looking great so it seems the partnership with KT really paid off. I wonder if they'll also work on future FE games? Either way hopefully Is learned useful things from them.