Because he's not a serious candidate. Congressmen don't get elected president. Period.
Let him run for Senate or governor. He needs to work his way up. You don't get promoted to CEO straight out of the mail room.
Historically, that is true. I recognize that it is unlikely that a congressman will make it to the White House.
However, I think you make a mistake in implying that the House is something of a lesser job than the Senate. They are different. Many have observed that the Senate is about compromise. You cannot be too idealistic in the senate. It just doesn't work. The House is different. It's big enough so that you can hold on to principles and still hope to accomplish things.
I want a President who puts principles first. I think being a senator is actually bad training for the job. But, as you say, voters seem more likely to disagree with me.