“yogis also realized the detrimental effects of sensory pleasures and developed Jhāna and Samāpatti to be reborn in the Brahma realms. However, they could not eliminate the Saṁyojana (fetters). Why were they unable to attain the wisdom needed to break these bonds?”
The answer is pretty much in the question – because they were unaware of Dhamma. Their yogic practice is the same as that of someone trying to get rich or do better in the material world for self-fulfillment. What I mean here the same ignorance of the true nature of the world is used for spiritual means.
