I've been trying to figure out that out myself, and it can't be because of space. There are several other tracks that run longer than those tracks did before they were cut down.
The two most infuriating things about the DK Rap being cut down are a) They cut out Lanky and Chunky's verses, even though they're unarguably the heart and soul of DK64, and b) The verses they did leave in, Tiny and Diddy's, are nigh-incomprehensible. Nice job, music department. -__-