The foot in those with diabetes is at a high risk of complications developing so they need to take good care of their feet.
There are a number of things that diabetes, especially if it is poorly controlled, can do to the feet. The damage that gets done to nerves means that feeling pain and other sensations are impaired. if there is any damage to the foot, or a corn or callus develops or an ingrown toe nail develops, or any number of foot problems, then because of that nerve damage they are not going to feel any symptoms or pain. The problem is going to get substantially worse before they might notice that something is wrong. A serious infection, for example, could be well on the way to spreading becasue there was no pain when it started to let them know that there is a problem.
If the circulation has been affected by the diabetes and is poor, then there are going to be issues with how any damage that is detected heals up and gets better. The circulation is needed to bring all the white blood cells and other chemicals that are needed to fight infections and heal to the area of the damage. If the circulation is poor, then that ability to fight the infection and heal is going to be more difficult.
It is for these reasons (and a number of others) that those with diabetes need to take care of their feet. They need to check their feet every day to make sure there is no damage. If anything is detected or seen, they need to act to get it fixed urgently. All sorts of preventative measures need to be taken to reduce the risk of a problem developing.