Is it partly because he's QEII's youngest child, and also that he hasn't really done anything controversial during his life? I'm too young to remember his childhood and formative years - did he get more attention back then?
I thought there was a chance he might assume greater prominence as one of the most senior royals, particularly with the events of the last few years - his nephew the Duke of Sussex departing as a working royal, both his parents passing away, KC struggling with cancer, and AMW now completely ostracised from the family. That doesn't appear to have happened though.