It's easy to understand, MK is not only Richard's boss but one of his best friends, so Richard wants to be available in case MK needs him. Before accepting a very long touring contract with other artist, we wants to be sure that his friend and boss is not going to need him.
Richard left Neil Diamond years ago to pursue a career as a session musician, so going back with him wouldn't had been a priority if MK would had toured this year, but as it's not the case, touring with Diamond AND HIS SON is a nice chance.