The cave heavens and paradises kept the people of the 3000 worlds ignorant of the ink because they feared people would be attracted by the ink's promise to allow easier level ups. But when the price is becoming a slave without an ability to resist, would it really be so attractive?
Also, the old masters are bloody slow to appear. What do they even count for? I bet they are now in their 20th meeting, still trying to decide what name to give to the possible anti-ink operation in the Black Prison territory. Ents are faster than they are.