I'm a vim fan, personally. The keyboard is ideal for high-speed, high-skill interaction. Most GUI-centric applications fail completely in this area, where a lot of old applications had a lot of focus on it. Both is probably the best, but that's hard work and doesn't always fit with the GUI without it being cluttered for a "clean" interface.
Think about how much people complain when Facebook change their UI. Now imagine that if when they changed their layout you weren't able to do your job because it took you twice as long to find some information or if you lost a lot of money because you missed a pricing alert. Users are opposed to change for many reasons other than complexity for complexities sake.
If your company is willing to shell out $2k/month to give you a Bloomberg you've got other stuff you can brag about far more than the fact you can use a complex piece of software.
But I imagine the real reason they haven't done anything is simply because it's not worth it. Investing a huge amount of money (we're talking in the high tens or low hundreds of millions here) to revamp your GUI without a clear return on investment would be idiotic. They have been tackling the low hanging fruits though (the new graphs, font, etc.).
In that sense, it's very much in the spirit of any other command line environment. But apart from any UI issues, people continue to use it because of network effects. It's got a great messaging system that everyone uses, and it's got a common set of tools shared across the entire financial system.
Old habits die hard, too. Even though I'm no longer trading, I still have an old Bloomberg keyboard on my desk.