Matt nails it with the Blue Dogs:

After all, the whole motus operandi of the Blue Dogs, as described by
Robertson, is that they vote like Republicans and then tell their
constituents about it. That is, they convince their constituents that
when they vote for a Blue Dog, they are getting a Republican with the
power of a member of the Democratic majority.

[snip]

Blue Dogs get a great deal by being part of a large majority, with a
large enough bloc of coherently unified conservative ideologues who
frequently bring the Democratic Party to its knees. They get millions
of dollars of cash from the DCCC to support their re-elections. And
they get this backing from the party, often in districts where if they
ran as Republicans they would likely face strong primary opponents. Why
would these Blue Dogs be ready to jump ship from the Love Boat the
Democratic Party has them sailing on?

And, for serious. If there was a Republican majority, or they could help make one, I could see the party-switching being a thing for different selfish reasons, but the current selfish reasons suit these fucksticks just fine. They not only get to vote their interests and make their asshole constituents happy, they also get to act martyred and put-upon every time somebody calls them fucksticks on a blog because it’s so OMG HAAAAAARD to be as centrist and sensible and normal as they are! The whole world is full of anti-war protesters with puppets who don’t want the banks bailed out and they’re so MEEEEEN.

Ideologically, 40 years ago these would have been Republicans. The only reasons they’re not Republicans are a) have you SEEN the Republican party lately, they’re repped by that Red State fool and the Tea People and b) being a Republican wouldn’t allow them to act so aggrieved while simultaneously cashing in.

A.