On August 2, Massachusetts Republican state chair Amy Carnevale, appearing on a TV interview program, said Massachusetts election law requires too many signatures for candidates to get on  ballots.  See this story, especially the fifth paragraph.

Massachusetts is the only state in the nation in which it is normal for only one candidate to be on the general election ballot for U.S. House.  In 2024, out of nine U.S. House districts, only two of them had a Republican on the ballot.  The problem is that the law requires 2,000 signatures per district.  No other state requires such a high number of signatures for U.S. House to get on a primary ballot.

It is unheard in the other five New England states to have one-candidate U.S. House general elections.