I believe that this is the premise of the "Right to Repair" movement. There is no valid reason for the software to be that expensive other than to prevent competition in servicing the tractors or to gouge the consumer for minor repairs that they could easily do themselves. Both are unethical and skirt on being illegal. They could open up the diagnostics portion of the code but block users from tampering with the emissions related settings. Not saying I agree with this, just stating that it would be possible. I had heard that there is someone in CZ that can make your 45 HP Kioti a 55 HP using standard settings (the 45, 50 and 55 engines are identical, it is all software), all the way up to 75 HP. I personally would not feel comfortable sending my ECU to some Czech hacker, even after I am out of warranty. But if I had a buddy that has a DK5510 and a way to download the bits into my DK4510? But that would be dishonest, right? That would be the justification they would use to keep it locked down.
About the only way that there would be a case against the manufacturer for improper pricing would be if they charged dealers some small sum like $100/year for software but charged somebody $10,000/year that they didn't want to sell to but were forced to sell to by regulation. However, it is reported that at least some OEMs charge their own dealers a very high price for these tools and software, so there would be no case against the manufacturer if they simply now will sell to anybody else at that same high price. The government generally cannot dictate the price a that a company can charge a third party for their goods or services. They can only dictate prices if they themselves are the customer. I will tell you it is miserable if you are on the receiving end of that "deal," particularly if the government is by far the biggest customer in the field and it is not only not politically advantageous to pay you, it is actually politically advantageous to NOT pay you.
And just to make sure everybody doesn't read me wrong, I am not an apologist for these large companies and do not agree with their tactics of trying to make everything unnecessarily difficult to repair. I am saying that I don't think that this policy will actually accomplish what most here appear to think it will.