The developer chooses if the price should be different or not. In that case, Youtube decided that the users should pay the 30 percent Apple tax.
> During a subscriber’s first year of service, you receive 70% of the subscription price at each billing cycle, minus applicable taxes. After a subscriber accumulates one year of paid service, your net revenue increases to 85% of the subscription price, minus applicable taxes.
Source: https://developer.apple.com/app-store/subscriptions/#revenue...