Does that mean if I subscribed for 22.99€ it would stay that way year after year?
What could be the reason that Apple designed it this way? The only reason I can think of is customer protection (say 1€ a month changes to 100€ a month and you user does not pay attention).
Your question implies someone "designs" things and given the state of the apple app store I'm not sure any form of conscious life is in charge of it