savings is an economics term. Typically, in economics, you have investment and savings. That is true in business also.
"In economics, savings is the amount that is left after spending. In
banking, savings refers to savings accounts, which are short-term,
interest-bearing deposits with a bank or other financial institution."
Often, when discussing investments, one investment (money spent) will be compared to another in terms of how much less you might spend on one rather than another. The savings (money not spent) in investment A can represent some amount when compared to investment B. The term in this context is always in the plural. One always looks to spend less and make more.
Also, in terms of personal finances, people refer to the savings with an s. This term is not about the possibility of saying "saving"; it is about the term used in businesses such as banking,finance and investment and in personal finances.