I get the sense that they're both seen as more or less equal "49 state Republican landslides". But this neglects the fact that Nixon actually did a fair bit better than Reagan, winning by 23 points as compared to Reagan's 18. If we look at the Democrats, McGovern did 3 percent worse than Mondale. This is a larger difference than the one between Jimmy Carter's "narrow" win and Obama's "decisive" win. What gives? Is it the similar Electoral College margin? Is it the similar-looking Electoral College map? Is it that margins are evaluated by proportional rather than absolute difference?
Mondale was a better candidate than McGovern was. He might have said some stupid things, but he had an actual campaign and did well at the debates, unlike McGovern he tried.