He decided to go to a fundraiser instead of Leonard Nimoys funeral. Essentially his entire fan base has disowned him.
If Nimoy was a full practicing Jew (and I think he was) he had to be buried before sundown the day following his death, which doesn't give a lot of reaction tme if you have other commitments. But rather than say he had contractual obligations to be somewhere else he could not get out of - Shatner stated he made a personal decision not to go. He would have still gotten some flack but nothing like whats happening.