I strongly suspect it's in the marketing, to make the bike visually fit the ad copy of the 25 to 35 hard ass sliding the rear tire around a gravel corner with bike packing bags on the bike (you get the picture) so to keep the wheel weight down and look you put less spokes. It looks faster this way.
Listen, I like alu frames and a lighter bike, so I don't have a problem with it--as long as they work for a reasonable amount of weight on the bike.
I'm sure too that the stock wider low pressure tires help the rims.