Why Do You Run Somone For Every Seat?
Because occasionally your opponent in a strongly Democratic seat, will do a lot of stupid things.  Like Russ Carnahan (D-MO). Here’s proof that every email you receive from you Congressman really is a form letter. h/t

Note to Missouri Democrats
If you want to play the “Roy Blunt was having an affair with his now wife while still married to his former wife”, keep in mind that two sides can play at that game.  No evidence of Blunt’s “affair”.  Robin Carnahan’s relationship with her now husband, however, seems to have been admited to by Carnahan