You don't cost them anything for not playing part of their game, and you don't owe them anything.
If your interpretation of why they do this is right, it meand they want you to believe that "modern content" is a reward for playing through the rest. Nobody should think like that. Playing the game is the reward for playing the game.
It's like if Netflix made you pay an extra as you start watching a series on season 4, because you didn't pay your subscription through the three previous seasons.
Honestly, no matter how much strategy you're using, Master Mode is not exactly balanced. The sword trials in particular become unbearable.