No offense, but you simply are reiterating your ignorance on the process.
None taken, but...I'm right, lol.
Perhaps a simple, but dissimilar example might help. You go to a car dealer and their MSRP is 50,000. You end up paying 40,000. Have they committed fraud? Have you been defrauded?
No because the seller simply lowered the selling price, which is not what we're talking about here.
Let's say you're interested in getting a loan for a new start-up venture. They want to know the value of your assets so that they can recoup things of value in case your new business goes tits-up and you can't make payments. Let's say your main residence is your collateral. On your loan papers, you claim you have a 4-bedroom, 3-bathroom, 4000-foot home; in reality, it's 3-bedroom, 1.5 baths, and 2 bedrooms.
I admit maybe not the best, most realistic analogy because most banks I know would probably insist on an appraisal in writing by a licensed appraiser - that's just another difference between a billionaire bullshitter like the Don and regular folk like you and me. If you're really rich, popular, and know the right people, I guess banks stop asking questions.
The banks should have done more due diligence, but my guess is they probably didn't because nobody in this transaction - not Donald, not the banks, not anyone - believed they'd ever be investigated, even though they all behaved shadily.