Yeah it's an American production alright. They're probably worried two guys wouldn't be enough to bring in demographics.
They are idiots. Both the recent RDJ movies and BBC Sherlock are extremely popular right now, and both kept the main characters male.
Okay, just to play devil's advocate, if there are already two
more traditional versions of Holmes & Watson out there, why would you want do the same thing?
Better to try something different to distinguish yourself from those competing Holmes series.
If you're going to go for a radical reinvention of the characters, you might as well go all the way . . . .