Some people sleep better knowing the "abandoned" software can always be taken up by other developers, because it's open source.

Others sleep better knowing there's a company with a financial incentive to keep the product alive.

Honestly, either way, I don't see where morality enters the equation. It's not wrong to release software that's closed-source, it's your choice as a developer. It's not wrong to give up some of your freedom, it's your choice as a consumer.