While I'm not a fan of the civil service system because it introduces a mandarin class the spoils system has its own idiocies. This sort of bad service was what original led to the creation of the civil service system.
A lot of these positions that are not obviously political but are held politically are held as non-obvious political payoffs in exchange for support. This was the entire genesis of the Travelgate scandal, the need to find additional slots to reward supporters. Presidential travel is a political function and serves at the pleasure of the President so Clinton had the right to fire them at whim, just as the Senate Democrats had the right to fire the preceding computer tech support personnel. Who gets that contract is a straight party line vote, always. It's not even generally voted on, the chairman just gets his way.
The reason for Travelgate being a scandal was the misuse of authority, consisting in character assassination of the previous personnel. The scandalous incompetence of the Democrat Senate leadership who viewed political jobs as more important than their own computer security has, to this point, remained a quiet scandal.