I imagine that it's because he delivered, rather than taking the time to abstract away stuff which might not need to be abstracted away.
Remember that very, very few organisations (companies or in academia) have 'quality code' as an overarching goal: rather, they want good enough code, soon. Time after time I've seen developers fall into one of two traps: abstracting too soon or too late. It's very, very difficult to avoid.
My preferred method is to just hack together something that works over a couple of iterations, then spend an iteration refactoring. It's hard to convince a business that this refactoring time isn't wasted, but it is in fact extremely valuable to the code base. 'I need to do this now so that I can satisfy your change requests later' sometimes works.