I was an underwriter for fifteen years, and have been in charge of all claims at my company for the past twelve.
It strikes me that you may be conflating a requirement of your leinholder as policy language.
Believe what you wish, but you are mistaken.
That would certainly make sense. If there is still a mortgage on the property, the lender would want to be first to benefit from the coverage, and would require coverage to be written that way in order to provide the loan.
But if you own the property outright, then you have more options open.
I don't use my insurance much, nor do I read the details in the declarations pages. I just know what I've said because a lady across the street from me had her house burn down. She wanted to take the settlement and move somewhere else. She couldn't until the house got rebuilt. Then she could sell it, take the proceeds, and use that to buy a new house elsewhere.