Consider: When was the last time the more experienced candidate won the presidency? The answer: 1988, over thirty years ago. Since the end of the Cold War, the less-experienced candidate has won every time. First-term Sen. Barack Obama trounced veteran Sen. John McCain, and political neophyte Donald Trump beat Hillary Clinton, touted as the best-prepared candidate ever to run. In 2000 an incumbent vice president faced off against the son of a former president, and the result was a virtual tie.
Moreover, the only challenger to unseat an incumbent president was also the least experienced. Bill Clinton, governor of tiny Arkansas, denied President George H. W. Bush a second term, but was able to dispatch a challenge from Senate Majority Leader Bob Dole with ease. Nor did Sen. John Kerry or Gov. Mitt Romney — both of whom had longer resumés than the presidents they challenged — fair any better, notwithstanding the relatively tepid popularity of the incumbents in question and the deep dissatisfaction with the country’s direction at the time. If the Democrats were to take that history to heart, and seek a nominee with even less traditional experience to challenge Trump, then apart from Buttigieg their only alternatives would be even less plausible: Andrew Yang, Tom Steyer, and Marianne Williamson.
With such a small data set any pattern may be dismissed as mere coincidence, but I suspect there is something real behind the phenomenon.