Q. Why the disc brakes are in the front wheel, but not in the rear wheel in scooters, can you please explain?

-- mostly it is done to reduce the cost. disc brakes r more powerful then drum brakes. but due to cost , the back side is not provided n is mostly drum brake.-- also the front tire has more stopping power then the rear tire. that y bikes with disc on both tires have bigger disc in front and smaller one at the rear.

Simple experiment try, Take long stick push it towards front it is hard, if you try to pull form behind its easy.The same in case all vehicles braking effects of front wheels better so powerful braking systems like disc used whereas drum brakes enough for back wheels to avoid unnecessary skid.