The biggest, best known online retailer reduced my credit line from $2500 to$1600. I haven't used the credit card in over 3 years. BTW, my current credit score is 843. Why does a company reduce a credit line when the account is inactive?

The biggest, best known online retailer reduced my credit line from $2500 to$1600. I haven't used the credit card in over 3 years. BTW, my current credit score is 843. Why does a company reduce a credit line when the account is inactive?