"If schurzen were introduced on pzkw 3L or M, then why don't all pzkw 4 use it?
Pzkw 4 comes after pzkw 3, right?"
wrong. the pz4 was developed as an "infantry" tank, first produced with the short 75mm (L24). there is not a huge difference in size between the 3 and 4. the pz4 actually...