On Offer acceptance there is either a contract generated or a pro forma invoice generated. Since the offer is binding once accepted, the offer if well enough detailed and advised can and often does take the place of the contract. Customarily in Real Estate transactions the purchase offer itself is generally also the contract for purchase as well. The offer becomes a binding contract once accepted.
LOI is fraught with many legal booby traps & pitfalls especially for the buyer. But probably the most damning reason why credible crude buyers would have little or no use for LOI in their buying dealings, is that using the LOI is fraught with many incalculable legal traps and pitfalls much of which could atimes be very costly for, and to the detriment of, the buyer, according to legal authorities and contract law experts.