I have been diving with Blue Angel for several years, and the first thing the DM says when everybody is aboard is "Where do you guys want to go today?" What makes you think that if every day the answer were to be reefs south of Palancar, they wouldn't go there? If the BA boats don't go to the south end every day, it's because we divers didn't want to go there.
Also and FWIW, some of my favorite dives are north of Colombia. If every dive you go on is south of Palancar that excludes 80-90% of the Cozumel reefs. For another thing, since the far south end is out of the lee of the island, getting in and out of the water can be difficult to impossible due to sea conditions and wave action on the southern "wild side" beaches can put so much fine sand in the water that the visibility on the far south reefs goes way down; there are some days when I wouldn't want to dive down there.