For me, there's a few reasons I still mess around with DBC:
1. I like that it's an interpreted language. You type, you run, you see the results without any compile time. Granted, compiled code is most often faster than interpreted code, but I can live with it.
2. One can run DBC on older machines/OSs without worries in general.
3. I like BASIC being basic. DBC is reminiscent of older BASIC languages. The command set is pretty large, but it's still a pretty simple straight forward set of commands. When variants of BASIC started implementing C like structures and classes and more and more commands, I felt DBC stayed true to BASIC - and kept it easy (relatively) to use. DBPro, while it still uses the same base command set as DBC, has so many more commands, so much reliance on additional plugins, it just doesn't appeal to me as far as BASIC is concerned. DBPro is a fine product, but it's lost a bit of the simplicity BASIC was designed to offer.
4. There's a challenge in using DBC. I feel a certain reward in figuring things out that may be dubbed as not possible with DBC - or at least not obvious. It's kinda like tinkering with an old car that you somehow keep getting to start up!
5. I've learned a ton of stuff about 3D programming, modeling, game design, etc. because of using DBC. So, it's a bit of a familiar friend.
Overall, DBC is a decent product. It could use improvements in the 2D area, and some additional camera control (like multiple camera) and a speed boost for the interpreter. These are covered in DBPro but I would want DBC to remain an interpreted language and not necessarily expand the command set.
Enjoy your day.