And when the manufacturer undercuts you and you're already bankrupt by the time the court case that the manufacturer's spendy lawyers will drag out long past your ability to pay...what then?
Given the choice between a private contract and government legislation, most companies would likely choose private contracts.
IANAL or a historian but from other discussions I read, I got the impression that, at the time, contract law wasn't as advanced as it is today. That's likely why it took a law to clear the way for franchises.
That's generally the case, yes. As one example technologists seem to like: California invalidates noncompete clauses at the level of state law, not through requiring every engineer to individually attempt to negotiate the noncompete clause out of their contract.
Contracts between power-imbalanced parties tend to be worthless. Any time one side can afford a legal fight and the other side cannot, you're really depending more on the integrity of the more powerful party than anything else.
That's the reductio ad absurdum claim that all too many HN posters would read of it. I am saying that when the gulf is wide enough that you can trivially withstand the other party's ability to seek redress (or, in the reverse, engage in barratry to force compliance regardless of the reality of the situation), they have no ability to seek redress and it is in that case that there is a valid reason for governmental action.