The rider availability argument makes no sense to me. There' s a limit to how many race days the riders can have anyway. No overlap doesn't mean they'll suddenly all do all races so the top guys will always meet. They'll still pick different races and miss each other.

What makes more sense to me is (unsurprisingly) the financial aspect. Two WT races on the same day will likely eat into each others viewership, making each less valuable to sponsors. No overlap should mean more total days with WT-races and those will always attract some viewership.

Although, of course, no overlap should result in a lot less weekend races? So who knows how that'll impact everything.