What I seem to see in the comments is that "X is their killer app". But actually you'll find they have loads of X, Y and Z apps. You just think that it's X because most people are in a particular product.

The breadth is quite amazing. No matter what I was trading, BBG had a foot in the door. Want equity analyst data? Check. Want to look at OTC bonds from various banks? Check. CDS indices? Yep. CDS single name? Yep. Want a swaption calculator? Yep, even got vol surfaces for that. What about FX exotics? Sure. Just about anything I touched, BBG would have data or calculators for. Sometimes you found the data might be a bit sparse, but they'd have some upsell for you if you liked.

As for the APIs, there is a lot of digging if you're going to use the data for anything. Finding out exactly how some data column is collected is hard work, they don't make it easy to ask. You do have the upside that almost all data is collected the same way, so you don't spend a lot of time writing several download APIs.

There's also a lot of settings that affect the data that aren't obvious. Well perhaps it's in the documentation somewhere but it definitely helps to have someone around who has seen the quirks.