Why aren't representatives typically seen as presidential material?

[President Johnson]

With all this focus on Beto and some guys both in the media and the Forum, why aren't House members typically seen as "qualified enough" to be president? That's not the case with senators, even though I know only the senate approves presidential nominations. But putting thumbs up or down for some cabinet secretary or judges can hardly be seen as much presidential training. Of course, a senator's vote has more individual impact and he usually represents more people, but representatives usually won more elections since the have to run every two years; sometimes in swing districts versus safe states for some senators. (By the way: The mayor of New York or Los Angeles also represents more people than the governor of Delaware or Montana).

I personally do believe that governors are, at least on paper, best qualified for the job, especially if the have some legislative experience in congress or at the state level before, and maybe a private sector career. But wouldn't say a congressman is much less qualified than a senator, especially when he or she served for a couple of terms. Beto for example would have been in congress for a longer time than Obama when was elected president.