" So offering something for free and then rescinding later is treated worse than never offering anything for free at all!"
This is true plenty of times. In particular, if you violate social expectations/etc, you will often see this.
For example, here's an easy case:
I am about to go plant a bunch of trees.
A neighbor sees me going to do it, and offers to do it for me for free, because they like to do it.
I say cool. They can even say "just so you know, i'm not your contractor, blah blah blah" or whatever. Doesn't matter.
I go do something else with my time.
A week later, they did half the job, and quit, or they did the whole job and made a hash of it, or whatever.
1. It wouldn't make sense for me to expect them to fail or stop doing it or do it poorly just because it was free. Nor plan for them to fail.
2. Most people would still complain even though they paid nothing, and are arguably no worse off (depending on the options you pick) then when they started.
3. Most people would definitely feel like it was worse than doing nothing.
Now, in this example you could argue it's the poor quality/stopping halfway through that is causing this result, but you would IMHO see the same result even if they did a great job, but stopped after doing 90% of it, leaving me definitely no worse off, and probably much better off.
In the end, people's expectations are emotional and not simply rational.