Production code is an asset, its maintenance and obligations are an expense, its risks might become liabilities, and companies shouldn't run more code than they need for the same reason they shouldn't own a larger vehicle fleet or more spare warehouse capacity than they need.

I don't think most engineers really disagree with this. Saying code is a liability is technically incorrect but pithy shorthand to communicate that it comes with the associated baggage of maintenance, obligation, and risk; these things suck up money the same way a liability does. Tech debt is also not real debt. It's a figure of speech.