I'm not sure why the public have voted for him so consistently. He seems a nice chap but really!!!!
'Vote for your favourite' ~ that's the tagline I think, isn't it? So presumably a lot of people prefer Bill to Ranvir, for whatever reason (they were fans of his beforehand, they're massive fans of Oti, they're a similar demographic and like seeing themselves represented on the show, they think he's a 'nice chap' (to use your own words)).
I've got nothing against Ranvir at all. She did some nice ballrooms routines and had a lovely 'feel' to a lot of her dances. But she was pretty poor at anything that required a bit of pace or that wasn't in hold, she never seemed to have much energy or enthusiasm about her, and the 'timid, older, single mum finding her inner goddess through dancing, with a side-order of fauxmance' narrative started to get nauseating after a while.
The show really isn't a dancing competition: it's a light entertainment show disguised as a dancing competition. But, that said, I'd still say that taking the various dance styles into account, Bill is a marginally better dancer than Ranvir. His Latin is far from perfect, but he makes a bloody good effort.