It could simply be natural hormonal changes that have killed his sex drive. It happens to quite a few women, too.
This can lead to totally all avoiding non-sexual closeness, because they lead to the partner wanting more than is on offer.
Once that sexual drive has totally gone, both physically and mentally, you are probably no more likely to reawaken it in that person than you are to 'awaken' it in a pre-pubescent child, and the thought of non-penetrative acts can have become as unpleasant as the full act, regardless of how much that person loves their partner.
It is not a deliberate choice, but no amount of parading around in sexy lingerie - or birthday suit - is going to change that.
Each individual case is different, and obviously it's best that the 'sufferer' is checked out at an early stage to see if there is a clear cause that can be remedied, but that is not always possible.