Because this is the biggest lamb shoulder I have ever come across. It came in what my local butcher call a 'surprise box' i.e. you've got no idea what's turning up because it depends what's in the shop at the time.
I don't eat lamb, but DH and the kids do. DH will eat almost anything and has a penchant for very spicy foods, the children less so. One of my children isn't too fond of chewing meat (he has additional needs) so anything that wont turn it into shoe leather would be fab