After losing 30 kg through diet my fasting blood sugar went down from 100-110 to 75-80 (no medications). how did weight loss make that happen?

Insulin sensitive: As you lose weight your body becomes more sensitive to Insulin (less Insulin resitant) so that the same amount of Insulin made by your pancreas does a better job to get the sugar down, both before and after eating.

Insulin sensitivity: As you lose weight your body becomes more sensitive to insulin. As you gain weight, your body becomes more resistant to Insulin and has to make more of it- to absorb the sugar in your diet. With weight loss, you now have a normal blood sugar as a result of increased sensitivity to your circulating Insulin level.