BT's moat is data. 40 years of data engineering, building relationship with data providers, consuming direct exchange feeds, building proprietary data sets, normalizing and cleaning decades of historical data. Displacing BT is a gargantuan effort.

It's Emacs. Well.. not exactly but I bet an Emacs user would Very quickly feel at home.

"The ui is hard to learn" is a selling feature not a problem. It's like sabre or amadeus: it helps the industry keep out time wasters and maximises the agents sense of skill and value.

The socialised effect of "trade in Bloomberg or get a worse deal" probably makes the alternatives very niche.

If something like the LME had developed a terminal I could see it having the same value to it's community, or the bank settlement systems. Something used by most of your cohort, easier to stay inside it.

It's contract enforced API access. Illegal scrapers risk being excluded. If you pay the fees you get the spec apparently.