Voting districts should be drawn according to a minimum/maximum population.
There were more people who voted democrat (52%) in the last presidential election.
There were more states who lean democrat (26 out of 50) and thus Democrats have a slight edge in the Senate.
However, there are more districts that lean republican. The number of people in these typically rural republican districts is small... Comparatively a minority on a national level and in most cases on a state level. But the House of Representatives is determined by how many districts you control. Not your total number of votes.
The House of Representatives is a failed political model where a minority can yield a proportionally greater power, simply by building more trailer parks out in the desert.