I can jump in on this because, as an Enfield modder, I have been fielding this question for a decade.
Question:
Why not just buy a faster bike?
Answer:
Because my bike has certain style and characteristics which made me choose it over other bikes, and I want to keep it, but I'd like it to be a bit faster for wahatever reason. Other bikes don't suit my tastes, so they are not candidates just because they happen to have more power.