How so? Brown voted the way the people who voted for him wanted. The problem was that a lot of Democrats who stayed home in 2010 came out to vote in 2012.
It's not like there was some vast constituency of conservative voters in Massachusetts who felt disappointed by Brown and stayed home or voted against him. The people who voted for him knew more or less who they were getting and weren't bothered by that.
You understand, there is no real GOP in Massachusetts any more than there is a real GOP in, say, Philadelphia?
I guess not, but why assume there are a lot of "real GOP" voters there?
The point is, it would be an interesting exercise to find out if there are conservatives in Massachusetts by fielding a conservative candidate. For once. There's certainly nothing to lose.