Once you start learning C++, you'll see. Trust me.
GDK has the backup of C++, which has the flexibility of Object Oriented Programming (using the class, struct, and union keywords), inheritance (inheriting the qualities of one class to another), template classes and functions (customizability), organizing you code via header files and translation units (c/cpp files), using other SDKs (GDK is one of many of these), and many other features that'll give a boost to your game's performance, as well as flexebility to it's development.
Of course if you don't know very much C++, and if what I just said was a million miles over your head, I would strongly recommend getting started with DarkBasic Pro. It's going to be beneficial in the long run and a good stepping stone to your programming knowledge in the future. Along with this DBP has a large support base right here at the forums, as well as many tutorials that are fairly easy to understand. Diving into advanced game development really isn't going to do any good, I've seen many people get scared away by C++'s complexity and assumptions.
Hope I didn't just scare you away with all that.