Theft is not monetary because you didn't take money away from the creator, hence there's no "theft" in strict meaning of the word. It's like saying you stole money from the store because you didn't pay for the apple. You stole the apple, but not the money. Except in digital world, store would be able to duplicate the apple infinite amount of times, so intellectual property is not missing on the author's part, you just violated the law because you used it without compensation.

I understand the angle you are coming from, you are seeing it as potential income you have now prevented the creator from earning and phrasing it as theft.

Also, arguing about all of this is pointless, especially online. That's why lawyer is a life calling and not something anyone can just do as a hobby. Written law is always different from interpreted law and lawyers will try to twist and wiggle around meanings of words as much as possible, which is also the reason why agreements and contracts are written in such a way.