Where is the contract to return the shopping cart to the corral?

I always preferred people who didn’t, when I worked in retail. It generates a nice chill task (wander around the parking lot looking for carts). But if you want to do a favor for the faceless retailer, go for it. Mostly I chuck my cart in the corral to get it out of my way, but this sees more like a morally-neutral action to me.

Your analogy doesn't make sense. You are getting benefits from using the shopping cart and you bring back as it's expected as part of the exchange. You bring the cart back to where you took which is a low effort commitment entirely proportional to what you got from it.

Free software developers are gifting you something. Expecting indefinite free work is not mutual respect. That's entitlement.

The common is still there. You have the code. Open source is not a perpetual service agreement. It is not indentured servitude to the community.

Stop trying to guilt trip people into giving you free work.

In this context the social contract would be an expectation that specifically software developers must return the shopping cart for you, but you would never expect the same from cashiers, construction workers, etc.

If the software developer doesn't return your cart, he betrayed the social contract.

This sounds very manipulative and narcissistic.