Because it costs 15 fuel more yet hardly does better than a Sherman. Yet for 15 fuel more than the Panzer IV you get the Easy Eight which utterly dominates it. The Panzer IV is either overpriced or under-performing in relation to these units.
Comparing units cross faction is pretty dumb, yo.
They're in different armies and function very differently within them. Next you're going to tell me that the Jackson is either overpriced or under-performing in relation to the Stug or Firefly and the Luchs is way too cost effective compared to the T70 or Stuart.
Similar role doesn't mean you should make 1:1 comparisons. Does a Sherman have Pak40's to support it? Does a Sherman have Stugs to support it? Does a Sherman have teller mines to screen for it?
Cost is about controlling the time a unit appears and how frequently it can appear. It is not a measure of unit performance, although there is often a correlation between the two for balance reasons.