Well, one might ask the question "Why would they want the name Royal Enfield on the tank?" too.
It depends on how far each person wants to go to identify with the hardware, or scrub the identity off of it.
There's a lot of people who pay big money for a Rickman Enfield, or a Dunstall Triumph, or a Seeley Matchless, or an Egli Vincent, or a Dresda Triton, etc. They represent a step up from the OEM equipment, and people like to have the label on there.
Other people don't want anything on there.