I'm inclined to say that this applies to most of the losing Republican nominees in recent past: Mitt Romney, John McCain, Bob Dole.
I suppose this can in part be attributed to that odd habit of the American electorate to vote the less experienced and/or less qualified candidate into office (applies to 2016, 2008, and 2000 for instance), except when it's an incumbent president running for re-election.
The last winning, non-incumbent Republican nominee which I considered to be sufficiently qualified for the job was probably George H. W. Bush in 1988.
I think a lot of the reason has to do with how the dynamic in the post Cold War era was like but from 1932-2000 every President we have had were experienced and qualified with the exception of Carter and maybe JFK
FDR- Governor of New York and created a proto New Deal as Governor
Truman - Senator for 10 years
Eisenhower - General during WW2 who led allied forces to victory on Western Front
Kennedy - In Congress for 13 years before becoming President with 7 of those years being senator
LBJ - Senate Majority Leader and Vice President
Nixon - Vice President for 8 years
Ford - House Minority Leader
Carter - This is an exception and that was cause in 1976 in post watergate , voters wanted an actual outsider
Reagan - Two Term Governor the largest state in the union and despite having the Dems control the state legislature he got much of his agenda passed
HW Bush - Congressman , UN Ambassador , CIA Director , Vice President for 8 years
I think the post Cold War landscape changed things in which voters want someone outside of Washington
