I suspect that diabetes plays a role because inflammation may be more common, and the tendon is likely stiffer than in a non-diabetics hands which also increases the likelyhood. The real problem with having higher or at least more varied bg levels is that this scars red blood cells and they are stiffer, therefore less able to get through the smaller capillaries, decreasing bloodflow in the extremities, kidneys, eyes and heart.
How that affects tendons I’m not sure, just suspicious.