Do we know why he has stopped playing live shows?
Apparently after this question was posted Buckethead announced tour dates for April to June 2016. In the linked article, it says about Buckethead that:
Since he stopped touring, he’s released a staggering 224 albums as part of his long-running Pikes series, including an unfathomable 118 last year alone.
Though it's not an official explanation, I could imagine that he was focusing on recording and releasing an insane number of albums rather than touring.