The reason is that some of the fees are fixed(not a % of the loan amount) and this creates a situation where the fees are a high % of the loan amount and approaching predatory lending.
Some credit unions will gladly do this. And I think BofA still does them.
Average mortgage broker will likely shy away from this.
If you go to my site that talks about the "best note" and show it to the property seller and they implement the ideal criteria in combination with well prepared documents by qualified professionals then they can get more for it if they decide to sell it to me.
If you have any questions please ask