When the message isn’t born of social consciousness, it’s generally born of self-aggrandizement and cocky posturing. Either way, it’s fucking horrible to watch, even worse to listen to, and does it a disservice to actual poetry by calling itself “poetry”.
Of course, not that many poets read their work that well. Often it's because the poet doesn't have a very good voice, or doesn't really know how to read aloud in public - it is a skill, and like all skills must be mastered, and it is mastered through practice and rehearsal. There is also the problem that too many poets' poems are made up of words that are merely written, whereas the best poems are grounded in the spoken word.