Here's why:
* You can have more than one: You can have one appliance, two appliances, three appliances, etc.
* You can count them: You can say "I have five appliances in my kitchen."
* You can use the plural form: The plural of "appliance" is "appliances."
Example:
* Uncountable: "I need to buy some furniture for my new apartment." (Furniture is uncountable)
* Countable: "I need to buy two appliances for my new apartment." (Appliances are countable)