I think most of your questions can be answered by realizing that Bloomberg was founded in 1981, and they basically got a monopoly in financial data provision because there were no other options in 1981. That is why they have a custom monitor & keyboard: in the days before the IBM PC, everyone had a custom monitor & keyboard, because these things were not standardized. Bloomberg was a technologist & businessman before he was a politician; his business success gave him the money to run for office, his office doesn't force people to pay for Bloomberg.

The reason they're still a monopoly is because knowing how to navigate a Bloomberg is a critical skill for most finance professionals, and now that they have that skillset, they can be very productive moving around in it. A different (better?) UI would require they re-learn everything, which is not going to happen. And when financial professionals are making half a million a year, paying $24k/year for a terminal so that they can be productive isn't a bad investment.

(Source: have a couple friends at Bloomberg. One is in their UI department, and keeps having his proposals for better UIs shot down for business reasons. Also married a financial professional who had to use a Bloomberg in her days as a bond trader.)