The obvious answer is Dem hackery.
But there's also the fact that most of the time a Senate challenger is going to have far higher name recognition than a House challenger does because the races are much higher profile.
If it is just an issue of name recognition, then isn't it even worse for a Senate incumbent to be below 50? That would suggest that a House incumbent that is below 50 may be able to pick up some support simply by running some ads and increasing name recognition.
Most of the time, the more evenly matched the name recognition, the more representative the poll will be of reality. I'd rather be leading by 5 with my opponent being just as well known as me than leading by 10 with my opponent being a complete unknown, especially if they're a serious candidate that has the resources to eventually get their name recognition on par with mine. For instance, the name recognition gap between Claire McCaskill and Josh Hawley is far smaller than the name recognition gap between like, Peter Roskam and Sean Casten. In fact, in the former case there basically is no gap at all.
