I eat one meal a day but I still don't lose weight. Why?

Bad technique. Eating less frequent or skipping meals slows down your metabolism which is counterproductive to achieve weight loss goals. Instead, one should eat low calories meals but frequently, i.e., breakfast, snack, lunch, snack and dinner. This will help you achieve your weight loss goals which appear contrary to your thinking but it works.
Need diet & exercise. Make sure you exercise at least 30 minutes a day, don't skip meals, avoid soda, juice, dairy, alcohol and fried foods. Eat a healthy well balanced diet! also water, organic vegetable broth, green leafy vegetables, natural pickles, apples are great to fill you up so you dont feel hungry and they are very low in calories.
Adrenals. Body goes into a slower metabolism if you eat less. Adrenals need adaptogen to shift then from stress mode which makes us gain weight around belly - if you take adhs (vasopressin) by biotics this has little tyrosine and other adaptogenic herb that boost metabolism and kick starts the weightloss effects.