Hoa…
Your experience is vastly different from mine. I have 32 years of experience, mostly (~95%) consulting for public agencies in California. I have worked with the US Bureau of Prisons, the US Navy, the California Department of Corrections, and numerous counties, cities, and special districts. I can't recall ONE instance where an owner (public or private) wanted out-of-scope construction work done for free. I have helped resolve scope of work disputes, but if the work requested is determined to be outside the scope of the construction contract the owners have paid for it without too much fuss.
On the other hand, I have had owners request (mostly unsucessfully) that I provide out-of-scope engineering services for free. The mind-set seems to be that since construction is tangible and visible it ought to be paid for, while engineering is intangilble, esoteric, and maybe even magic, and thus has little to no real value worth paying for. The worst case of this I can remember came from a Grade V wastewater treatment plant operator who sat on the board of special district I consulted for. He had worked with engineers for ~30 years, but was so clueless that he asked me questions like, "Aren't all engineers the same?", "Can't you just push a button on your computer to get the design?" (I wish), and "Why can't engineers eliminate change orders?"
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"Is it the only lesson of history that mankind is unteachable?"
--Winston S. Churchill