Because twenty years and change ago we decided it should be illegal to crack software. Except we didn't say that, we said that any code that controls access to a copyrighted work has special legal protection. Specifically...
1. You can't legally break such code, unless it's for a handful of statutorily or administratively selected purposes
2. You can't legally tell people how to break such code for any purpose
This provision is part of the DMCA, section 1201. It was policy-laundered through the WTO into US law against the objection of the tech community, so basically every country has the same rules.
The problem with this law is that it's scope dramatically extends past it's intent - hell, half the original law is just exceptions intended to control the extremely broad scope of "no breaking digital locks". What people realized was that they could put DRM on anything, regardless of if copyright actually protected it or not, and it would still have the same effect because DMCA 1201 has horrific chilling effects. Even if SCOTUS says you can't use DMCA 1201 to protect, say, printer cartridge DRM; that decision still took 10 years and millions of dollars in legal fees to reach. No company wants to spend that amount of time and money just to gain access to repair aftermarkets.
On the other hand, the law regarding price gouging is very old and well-established; because it's a very long-running problem. Serial-locked parts were basically unheard of outside of videogame consoles up until this decade. The assumption with DMCA 1201 was that it was going to keep people from copying DVDs, not from repairing tractors. It's one of the few cases in which the law actually needs to catch up to technology (as opposed to someone trying to get away with something and parroting a thought-terminating cliche).