What do you mean by free? Completely free as in Mad Max? Because unless you mean that free, then obviously there are some rules.
Now, I don't think measuring the effectiveness of those rules, to maintain the efficiency of the market, should have much to do with cardinality, but you're right that just adding more rules to handle edge cases simply leads to a more complex and likely more fragile ecosystem.
> How did one company get so big and change all the rules in farming?
How did all the usual automakers got away with the same copyright/DMCA hard-to-repair shit? Market forces. Race to the bottom.
> It’s hard to believe John Deere is the only company to buy from
Likely there are others, who likely pull the same shit.
> If that’s the case shouldn’t they accept the product as it instead of trying to get legislators to change the rules?
Of course this is a possibility. Or they can start their own company. Or they can ask other established machine manufacturers to venture into farming machinery hoping that that will help. And so on.
But basically what's happening is this group of farmers discovered politics, and they are now trying to persuade society/legislators/regulators/power-brokers to fine tune that "freedom" to include repairability.
Basically it's an economic argument against rent (in the economic sense). Because these buyers argue that they are basically in a quasi-monopolistic market, and thus the profits extracted from them (via these stunts) are a lot higher than they should be.
Of course we can say that who cares, just raise the price of produce, grains, etc... raise the already enormous amount of agriculture subsidies, let John Deere pocket this extra. After all, it's on the stock market, apparently there's no big private stockholders, majority ownership is by a bunch of funds. (There's a ~10% private equity too, it seems.)