Because "Learning a new system is hard" is the number one "Why I can't play anything other than D&D" excuse that I hear. Followed by surprise and disbelief that most games don't take multiple sessions to learn.

They made their DnD and it was cumbersome to learn, then someone in marketing did their magic. To believe they did it on purpose requires a certain amount of belief that if they tried to do that, it wouldn't end up unplayable.