What all of this will come down to is sponsors and the value they get from their riders.
Put the world cup behind an increasingly expensive paywall and you're guaranteed to get less eyes on your brand , PLUS you need to sponsor riders / teams that are guaranteed a place in the competition.
Whereas Hardline / Rampage / Crankworx are free and easily accessible , get half a million views to the live stream and maybe double that after the event as well. Plus there's all the media leading up to the event , even more exposure. I don't care what numbers WBD claim for their viewership , there's no way they're coming close to RedBull on their site and Youtube.
Time will tell , take eyes away from your "prestige series" and it's value decreases. We'll see at the end of the season I guess.
My 2 cents.