Question

Why cant ac current be used for electrical appliances?

Answer 1

Electrical appliances like motor, water heater, fan, waste burner, shredder etc. use AC supply directly.  So AC current is used for such appliances.

But many appliances have electronic controls and have the latest technology control panels and facilities for convenience.  These electronic (semiconductor) based circuits use a steady and small voltage DC supply.  So the AC voltage has to be stepped down using a transformer first and then converted into DC using a rectifier.

Some of the appliances need a steady DC voltage to do the function. There AC cannot be directly used.  A computer needs a DC supply for example.