The problem in Academia is that its too crowded. With crowding, in many fields, the de facto way to progress has become to play corridor and department politics. I know completely clueless and incompetent researchers that made an effortless transition to faculty positions at top 10 universities, whereas some great postdocs were stuck forever, burnt out, and left. Ironically, some of said postdocs did the work the others took credit for in order to be promoted.

Some fields are more prone to this kind of behavior and power structures than others. Plus, in the past, it was much easier for recent PhD graduates to progress to tenure-track positions, without needing to do a postdoc (or many!) in between.

Actually, some countries have established regulations to try to prevent postdoc abuse, as faculty is typically interested in getting them to do all work, giving them little credit, etc. Some of my postdoc friends were supervising students, designing studies, and writing grants but their names were never officially on paper! Their PI used this as a way to getting them trapped. Without e.g. supervision experience, they would not be able to move to tenure-track positions, thereby getting stuck with him (as cheap labor) forever.