The GOP didn't even try to take that seat; I guess the party preferred to concentrate on the governorship and open Senate seat. The first I heard of the GOP talking about the MD-03 was on the week prior to the election, and obviously it was merely disinformation to see if the Democrats would get distracted from the gubernatorial and Senate races.
Didn't you talk about the calculus of a Republican win in MD-3 a few weeks before the election?
Anyway, I agree that the Republicans never took it seriously and that 33% is misleadingly low. That said, Cardin was known to be abandoning the seat very early in the cycle, before anyone knew the election cycle was going to tilt so strongly 'RAT, so it's surprising they didn't even make a feint toward contesting the seat if it's as competitive as some would argue.
I don't know what makes a 45% Bush seat (2004) as uncompetitive as this one turned out to be. But I don't know Anne Arundel County.