Exactly, those are admissions stats AFTER weeding, they would be far lower if weeding did not occur.
This rather famous study found that only about 16.5%, or one in six, of the people entering college with the serious intention of following a pre-med track actually ended up graduating with the necessary courses to apply to med school:
OK, so hypothetically, what if those other five in six actually did apply to med school? Those admissions rates would have to drop to one-sixth, so it would be something like 6% of applicants getting into any med school.
That would be a horrific waste.
The bottom line is every year, there are far, far more people starting college with the goal of attending med school than who can possibly attend med school in the future. So the vast majority of them are going to get weeded out either sooner or later. And in most cases it will not be doing them any favors by making it later.