GOP Senate Candidates Skipping Convention

"Nine of 12 targeted Republicans running in the most competitive Senate races this fall are either skipping the Republican convention in St. Paul, Minn., or have not decided whether to attend."

Is this merely a product of their being in tight races and needing to spend time back in the district campaigning?  Or is this an example of candidates trying to stay as far away from the GOP brand as possible??  My guess is both.  If the GOP brand were popular, attending the convention could boost a candidate in a tight race.