As someone who writes both rap and "traditional" rock lyrics, I have a deep respect for both writing styles. Rap is very hard to not be boring while rapping, in that usually you write 3 16 bar verses for every song, so not repeating yourself can become a challenge. Changing up the flow and such also requires some thinking. Rock is the exact opposite, sometimes trying to express a full idea when a verse may only contain 25 syllables, not even words.