Whatever the media's motivations, it really is the right thing to do.
Your politicians work their way up, councilman, mayor, or district attorney, governor, etc.
If you have limited resources, and you scattershot them all over the place, you'll just continue to lose, and you'll never have a network either.
By starting at the grassroots, and concentrating on a race at a time, you win, then while there (and before) you start to build up networks, eventually, you have a pool of canidates for higher office, with backgrounds, built in fundraising, a track record of results, and a GOTV network of voters and volunteers.
If you run guys at all levels, dividing up your resources regardless, you may get a moral victory, which, along with 50 cents, may just get you a cup of coffee. If you work from the grassroots and locally, you'll actually get guys into office, who can now run for higher office.
Save your breath. Third parties have blueprints for building a house starting with putting the roof together first. What about the foundation, you say? Screw that! Start the house with the roof first.
It's the "principled" thing to do. </S>