Fire Emblem has had an abnormal amount of Fanfiction for its audience size, showing that this is an audience that is readily interested in the chemistry of the relationships present in the game.
Not just Awakening either. I've seen a ton of fan artwork of Path of Radiance/Radiant Dawn characters being together; romantically, and non-lewd too. Fire Emblem support systems has always been something people liked because it gives them reasons to like the characters more. Awakening isn't more popular because it's lewder - it's more popular because they doubled down on the support system and relationships. Easier to get support, less restrictions, and you can ship any hetero pairing and have them have kids too!