On top of that, good luck buying a place with a mortgage/20% down payment. A friend of mine was turned down multiple times trying to buy a condo last year because the sellers were only accepting all-cash offers.
A mortgage requires approval by the lender after the terms are settled with regard to the particular property (often including a third-party appraisal by someone approved by the lender to validate that the value of the property, rather than merely the sale price, has the correct relationship to the loan value), which means that an offer contingent on a mortgage can fail, whereas an "I have cash right here to pay now" offer cannot fail.
but more importantly, once a deal falls through and you relist the property, the price can potentially be negatively impacted for a variety of reasons.
I take it those load deals entail some risk to deal completion due to the bank requiring due-diligence and making sure the house isn't an absolute lemon?