The Ferdinands were made from the chassis of Porsche’s failed Tiger 1 proposal. It was more a stopgap measure taking advantage of existing stocks. Many of the German tank destroyers and self-propelled artillery pieces were cobbled together from old Panzer 3, 4 and 38 (Skoda) chassis as well as captured French tank chassis.
By late 43 I expect the Germans were using whatever was on hand.
In operation Barbarossa the Germans lost 2839 of 3350 tanks. Kind of hard to make up that kind of numbers.
It didn’t help that Uncle Adolf constantly interfered in weapons design. He personally kept the jet fighter out of production until too late and hated the German assault rifle (sturmgewher?).