Why are calories different for people?

Metabolism.

Metabolism and/or burning calories.

It might feel like it's going super slow, but as long as you're at a deficit you will go down in weight. 2000 is a good number, keep it up!

I started this diet last January. I lost 20 pounds the first month, and 50 pounds in 6 months. It's taken me another 6 months to lose 5 pounds. I've tried walking 4 miles a day. Riding my bike 10 miles a few days a week. Weight lifting, and constant dieting. I've tried 200 grams of protein on lifting days, and little carbs every day. Still nothing for 6 months.

The calories aren't different. How and when the body is using them is different.

As stated, not everyone has the same metabolism, and other than differences in activity level, it’s also often based upon genetics. It really isn’t fair.😒