I think you have confused adjuncts for "lecture" positions or other "visiting" faculty.

Generally, adjuncts are (very) low paid contract workers- maybe $2k-3k for a 4 credit course who are not expected to publish (they generally have little to no access to university research resources, not even an office on campus!, so publishing is largely impossible) and have no real upward mobility. Most adjuncts work some other full time job (they have to- a full adjunct load generally pays less than 20k a year). These positions aren't supposed to lead to upward mobility within academia.

In some disciplines, there are other non-tenure track positions (lecturers, research associates,etc) which are early career positions (in particular, they tend to come with some access to university resources, so that publishing is at least somewhat possible.) These on top of postdocs, which are early career positions.