Funny thing is, if he actually had been as accomplished a dramatic actor as many non-political and even Leftwing movie critics believe him to have been, then he probably never leaves the industry. Gary Wills reckons his work in Dark Victory and Kings Row is overrated, yet you have people like Scorcese who say it's great acting. That those rolls dried up for the Gipper after the war, I think that leans towards Wills being right.
Otherwise, RWR having a fifties Western career renaissance like Randolph Scott, that probably satisfies him enough not to want to channel his energies into GE Theater, thence to GE itself, thence the Speech, '66 and all that.