Is it possible Allred is internally upset with the direction of the house Dems? I mean why else would an only 3 term Democrat give up his safe seat and probably lose to Cruz in the Senate race? It's also possible he dislikes the job of being a represenative and views potentially being a Senator as a more enjoyable position despite the risks of not winning the seat. It's worth noting Beto was also a Representative for 3 terms when he ran for Senate, but in Beto's case he did it for the national attention and to become a household name. I don't think Allred has the same intentions as he isn't a media seeker.
1. Because he could pull off an upset. People said what they are saying about this race regarding GA 2020, and we know how that turned out.
2. It could help build name recognition ahead of a bid for Governor or another run for Senate in 2026.