The problem isn't "I dOn'T kNoW wHo ThAt iS"; 13 of his 14 albums have hit #1 on the UK charts, and he won GQ Men of the Year awards in 1998, 2001, and 2012.
You're just uncultured. Which is fine.

It's that his fans consist exclusively of 50-60 year old Mums and Robbie himself.