It is because high blood sugars can cause nerve damage (neuropathy) which normally appears first in the feet. Your feet are checked to make sure this isn't happening. They will check the pulse to your feet, and also use a prong thing to check you have feeling in your feet.
Because your blood gets thicker with sugar. If you any have circulation problems then the things that might suffer are the extremities and the the things that they rely on which are very small arteries.It's not that feet are damaged any more than any other organ but they are one of the first things to show that there is a problem
The NHS check your feet and your eyes as an early warning.
If you lose feeling anywhere in your feet and you stand on something sharp ... cut it knock it etc but don't feel anything then you could have an infected foot in no time and not know it.
Some diabetics lose their feet ... then their legs because of this.
You should never be afraid to ask questions of people.
Especially people who have your health your life your money in their hands.
Someone once said ... One of the most intelligent things a person can say is ... I don't know.
Because that means they are open to learning ... about to know.