Actors are paid to act; any agent can tell you that the script is the least important part to them. When it comes to the principal cast (which the sales and financing are predicated), unless I can call the agent or manager directly myself and verify, there is no real attachment. The exception being a Spielberg or a Scorcese whose stature in the industry could reasonably facilitate any star interest.
So, if a letter or document that nominally or presumably conveys the signer's "intent" or intention to buy, is essentially meaningless and worthless in legal terms, and is not binding on the signer or anyone, and CANNOT be enforced on him, then why would a respectable crude buyer, in the first place, want to waste its precious time and resources (or that of its expensive lawyers) to engage in such a fruitless exercise for the benefit of a seller? Especially for an unknown or obscure seller?