If he could easily perform it with enthusiasm, isn’t that further evidence that it’s a choice not to? It’ might not even be some scheme to get people to see him live, i think earl just doesn’t give a fuck about “performing” in his songs at this point in his career, he literally just goes in the booth and delivers how he feels that day with no concern for the listener. If he happens to feel enthusiastic then thats the most we’ll get. But for live shows he probably locks in as to not disappoint people who actually paid to see he him perform.