Anyway, I suspect part of the answer was that Stevenson was kind of an accidental governor. He was elected only once in 1948 defeating a Republican incumbent who had a huge backlash to him over his handling of this. He honestly probably would've lost if he had ran for reelection in 1952 anyway.
Stevenson was a national favorite of, like, educated liberals, who by this point had absolutely seized the Democratic nomination process (JFK, who was good at pandering to these people, would appoint Stevenson as UN Ambassador, which was an excellent pander), but he was indeed not necessarily very popular with the voters. The 1950s were arguably the first decade in which "educated liberals" were a real faction of the electorate -- complaints about the liberal culture of universities go much earlier (back to the 1910s), but my understanding is that there wasn't actually a bloc of voters like this until after the Second World War.
Funny to consider how the DNC making nomination decisions would go nowadays. We would absolutely have gotten Mayor Pete as the candidate in 2020.
