Question

why alloys are commonly used in electrically heating devices?

Answer 1

For a heating element, you want to use a metal with a high electrical resistance, and a high melting point (obviously). If this heating element is going to be exposed to air and/or water, it also needs to be corrosion resistant. Nichrome , which is an alloy of nickel and chromium, is usually a good choice.

Alloys generally have higher resistance than the pure metals that they are made of, because the alloy disorder of the atoms causes additional electron scattering.