Having made a game for LD in ObjPas, I'd say that the main problem in game jams is pre-existing codebase. Although the goal is to create a game "from scratch", it's obvious that reinventing the wheel is not the point - people are allowed to use existing libraries, and many competitions (including Ludum Dare) also allow for some personal, pre-existing codebase, as long as it's publicly available. Putting it otherwise: if you want to create a game completely "from scratch", jumping on bare SDL / Allegro, then yeah, fitting in the 48h limit can be tough. But if you have some rendering tools, data structures et cetera ready to get plugged in and put to work, a rapid start becomes much easier.