Hello Al,
Commercial registrations are usually tuned exactly towards a particular song or a genre. It's not just picking a style and a voice - there is much more work behind that, like setting-up the correct sound, activating features, splits, pedal settings and more. The guys programming registrations often spend quite some time researching the original song too - so it's not a task that is done in a couple of hours :-)
So people buy them because it saves them time and effort. They prefer to spend their time on playing instead of programming. And for some folks, registrations can be a great way to get inspired for a new song or an oldie they wanted to play for ages.
Hope that helps. Cheers, Roland