Spirit Seeking Lilies weren't a spirit herb that Ryu was unfamiliar with. In fact, it could be said that they were responsible for him living a long life despite being unable to cultivate during his first life.
On the surface, Mental Realm cultivation was useless to the lower levels of the cultivation world. Even to the higher levels, it's a mere supplementary skill. The secrets of Mental Realm cultivation were tightly guarded by Clans like the Zu Clan, so after their banishment and banning, Mental Realm cultivation fell to the very corners of Martial World society.