There is a lot of pseudo-science (read: crap that's so ridiculous you would expect a child to come up with it) on this particular subject. For an example, see #2 above. You'll hear people say things like it's from too much super glue on your inserts, or storing bowling balls on wooden racks. I've even seen someone blame it on using a hi-rev style. It's up to you to decide what sounds reasonably plausible. There is not, unfortunately, a universal, scientifically verified reason why bowling balls crack.
That said, the primary idea for why balls crack is that when exposed to heat or cold, the core/cover expand and contract at different rates, which can cause a ball to crack. This is why it is recommended not to store bowling balls in extreme heat or cold, not to leave them in the car, etc. This is based on actual science. Another possibility is poor quality control in the plant where the ball was poured. Impurities in the resin could potentially make it more likely to crack. People like to immediately jump to this one, which I encourage you not to do. I'm also not going to say there's any particular company to avoid...I'm just gonna say Visionary stuff seems to never crack, and they also had the absolute best quality control in the industry, bar none.
I don't know of any actual science that indicates rotating bowling balls is important, but I don't pay that much attention to the subject, so I might just be uneducated about it. I don't see any downside to doing it, though, and it's not like it takes much effort.