Why did Lee Majors not become a MAJOR (forgive the pun) star?

The Six Million Dollar Man burst onto our screens and was a huge show. Majors had looks, charm, physique, was good at action, whilst also possessing a nice comedic touch (as seen later in The Fall Guy, and much later in Ash vs Evil Dead). He was a household name for years, but why didn't he go on to Burt Reynolds kind of stardom? He seems to have been the perfect tough guy not afraid to make fun of himself.