I think the short answer is because that was their choice. As to why, my guess is they approached it more from a timeshare standpoint than a hotel standpoint and this is c/w the culture where a studio is aimed at 2 people, 1 BR 2-3 adults, and a 2 BR 4 adults. I realize that at Disney people often take the clown car approach because they're often just looking for a place to sleep.
Marriott tends to have a King plus a pullout in a studio with real dishes, silverware and cooking items. IMO this is a major upgrade from
DVC studios. We stayed in a Wyndham studio a couple of years ago with a King bed, true mini kitchen and even though the fridge was small, it was high end with an ice maker. We've also stayed in 1 & 2 BR that had no more than the Marriott studio I described. For those looking at staying other timeshare, make sure you truly understand what you're actually getting and not getting by independent investigation. Don't rely on the company website or just RCI.