Even Ronald Reagan had to accept a career GOP hack (Bush I) as his running mate in 1980.
Ronald Reagan, in 1980, first offered the slot to former President Gerald Ford. Ford demanded, as a condition of accepting the offer, to be “co-president.” Reagan said sorry, Jerry, hope you enjoy your retirement.
Reagan then called George H.W. Bush. Bush had been Reagan’s main rival for the nomination. He [Bush] considered his time in politics over. I think he was dressed informally and enjoying an adult beverage when he got the call from Reagan. It was a total surprise to Bush.
That’s how it happened.
Party bosses didn’t dictate Bush to Reagan. Reagan was the party boss.
Ditto Trump in 2016.
Nobody who has the wherewithal to win the Republican nomination for President of the United States is “dictated to.” They might make deals with counterparts in the Congress, but that’s a different matter.
Well that explains Pence and Romney Ryan.