Let forget about tablet computers for a moment:
If you aren't using a device that has a no screen (graphire, bamboo, intous-- what 85% of artists have been using since the early 2000s), you are relying on the hover function to tell you where you are and where you will go. You need to be looking at the screen while you rely on proprioception. So, hover acts like an aide in a digital workflow.
Throwing tablet computers into the mix, hover helps with the offset of the tip to screen since screens were much thicker in the past and this function was necessary. In the past, eh, 7-years or so, we've made a huge improvement in screens and off-set issues.
In addition, many digital artists grew up with the aide of the hovering cursor since a lot of pixel pushing is necessary in a digital work space (primarily anything that isn't rastor illustration). Alas, Wacom has decades of software and hardware development behind them, so like geshults said, there's still a camp of folks who just don't want to part ways with their wacom, probably because it's so ingrained into their workflow. A traditional artist leaping from paper to an iPad pro may not have this bias since they have, simply put, different motor skills (and probably work that doesn't require something as fine as anchor points). Another huge factor is Astropad is Mac OS exclusive and many artist are on Windows, where Astropad doesn't exist.
I wouldn't pack your wacom away just yet-- Astropad is great but it's still a budding piece of software. While they are actively developing new capabilities, Astropad is still limited to a select library of programs.
Phew, I hope I made some sense! I find this topic to be interesting and I'm sure a whole scholarly article could be written about this topic, unfortunately I am not that person, haha.