Reagan benefited from the hard choices Carter made, including deregulation of the transport industries (especially trucking, but also airlines) that made it expensive and hard for companies to get their goods shipped to market.

It was also Carter that appointed Volcker to jack up interest rates to end stagflation (that Carter gets blamed for, but inherited from Nixon). There's a (probably apocryphal) story that Carter asked Volcker if he could end the whole inflationary mess and Volcker said he could, but that it'd likely cost him election. Carter said do it.

Carter's deregulations (including many other industries, like allowing home brewing and therefore the entire microbrewery market) have mostly stood the test of time because they were market-oriented. Most of the deregulation that has happened since (especially under Reagan and Clinton) was more "business friendly" and has led to lots of financial crisis (savings and loan, long term capital, 2008 crisis, etc).

It didn't help that for all his character and long term thinking, Carter was a terrible public speaker. Even though I admire him, I never feel inspired when I see any video of him speaking as president. He felt unpresidential for the opposite reasons that Trump is - he feels too meek.