In addition to all of the other comments a good analogy I'd heard in the past is related to plumbing.
If 80% of the way into building a house you realize you want to swap the bathroom and the living room you'd be laughed at. The pipes are laid you and you'd have to drop back down to the 50% complete level to move them.
But this happens all the time in software. It's why so many projects get stuck at the 80/90% level. Because those defining requirements, and many times even engineers, don't have a concrete understanding of what is plumbing and what is finishing it's very difficult to know whether the ask is to hang wallpaper or move a toilet.
Such swaps happen all the time in construction. We call them "change orders" or "remodeling" depending on when in the building lifecycle they happen. In software we have not be good about figuring out which change orders are expensive.
I've been in construction, most of them are actually really cheap because the common/likely change orders are built in - want to add a fireplace: until the drywall is installed the cost doesn't change. Want to make a doorway bigger, no problem, it will cost you $20 + the bigger door. Want to switch the tub for a shower after the pumping is roughed in - $50 to move the drain and water pipes, but once the tub is installed you need to pay for the tub you don't use as well (it has to be broken to get it out). As you say moving the bathroom to a different ___location will be costly.
It happens remarkably often even in big construction projects, when requirements shift for political reasons or when something unexpected is discovered about the ground it's being built on.
If 80% of the way into building a house you realize you want to swap the bathroom and the living room you'd be laughed at. The pipes are laid you and you'd have to drop back down to the 50% complete level to move them.
But this happens all the time in software. It's why so many projects get stuck at the 80/90% level. Because those defining requirements, and many times even engineers, don't have a concrete understanding of what is plumbing and what is finishing it's very difficult to know whether the ask is to hang wallpaper or move a toilet.