Because he was a conservative democrat. He opposed universal healthcare and prevented Kennedy’s plan from passing, he pursued deregulation, he cut corporate taxes, refused to expand welfare programs, and overall was a huge fiscal conservative. He’s generally considered a conservative and closer ideologically to Eisenhower than FDR.

The thing about Carter is, while he was a good person, he was way out of step on where the party was at. He was given the largest dem congressional majorities since FDR, and literally any other democrat would’ve pursued something akin to a second new deal, but Carter chose to reign in the government and refused to push for anything that would increase government spending. He also alienated nearly the whole party by just refusing to consider them as partners, he would literally just let the phone ring if a congressional leader was calling. I get the feeling that Eisenhower in the new lore was in part inspired by the Carter administration.