Pre-approval means approved subject only to the appraisal of the property. Are you sure these were pre-approvals (there should have been a commitment letter) and not pre-qualifies, which can be as simple as your breath fogs a mirror and your score seems ok.
Usually a contract for sale has a financing condition and a time limit by which time a commitment letter must be provided. If the time has passed for that financing contingency or the contingency was removed the seller might try to keep the earnest money. If the bank gave a commitment and reneged there may be damages against the bank.