the reason is that once a letter of intent has been signed and an exclusivity negotiating period has been granted to a buyer, the leverage in the negotiations will swing to the buyer. the buyer typically will argue that it can’t agree to some of the key terms of the deal in the letter of intent until it completes its due diligence. the buyer will, of course, resist giving the seller a basis to terminate exclusivity early since the buyer will begin spending substantial resources on conducting due diligence and preparing documentation.