Probably because of the high fat content. The fat needs to render properly, which means cooking it more than the meat would otherwise need. If you’ve ever had a rare steak with a large piece of fat in it, you’ll know what that unrendered fat is like.

In addition, the high fat content keeps the meat from being dry, so “overcooking” it doesn’t have the same effect as less fatty cuts (this is also why you can slow cook ribs and some other cuts all day, while leaner cuts tend to dry out in a slow cooker).