There are many pros and cons to the abandonware issue.
Firstly, copying it definitely isn't depriving them of a sale, since the sale is impossible, so any financial loss argument is moot. The same if you weren't going to buy a thing anyway. Did checking out a bootleg copy make any tangible difference to the world? If not, it's a thought-crime.
However, say you made a thing, and didn't want people copying it, and you also didn't want to sell it to anyone, but people are freely copying it and enjoying it. Just because you weren't willing to sell a copy doesn't make it automatically ok for someone else to copy and/or distribute it. So, it's wrong from an author's rights perspective, since you now lose authorial control over the creation.
Also, enforcing copyright requires subsidies in the form of taxpayers' money. Companies want to make and sell products easily, but want someone else to pay for the IP protection system, which includes you if you pay taxes. The claim the protections are needed to make products viable, but that's just the same as saying that their product isn't commercially viable on it's own unless the deck gets stack at someone else's expense. The reality is that the price to copy something is really low: supply is high. IP protections allow companies to restrict supply which means they can boost prices and make more money. Things like piracy actually helped to create a better pricing situation for PC games. Blindly going along with the rules wouldn't have done that: obedience to the money machine only means they'll charge more next year. Loyalty is a supply/demand thing. If people are more loyal to a brand they'll "reward" you by upping the price until your loyalty is in equilibrium with their greed. Disobedience throws a spanner in the works.