The idea wasn't to make infringement more illegal, it was to take DRM removal tools off the market. There were already theories of secondary liability - i.e. "contributory infringement" - for aiding someone in an infringement, but the courts had refused to apply them to new copying technologies[0]. Copyright owners also hoped that this would make player vendors obedient to them far beyond what the law actually mandated.
In this respect, DMCA 1201 has been fantastically successful at terrorizing basically everyone into overcomplying. There's no concrete definition of what a copy protection scheme actually is[2], so you can point to any undesirable antifeature of a product and call that DRM. This is pure catnip to gaslighting control freak companies like Apple.
For what it's worth, if you put something uncopyrightable under a DMCA 1201 technical protection measure, it holds no legal value[1]. I imagine this would also apply to public domain works, so you can legally decrypt them. Problem is, I struggle to see a legal way to sell the tools necessary to decrypt such works.
[0] I'm specifically referring to the Betamax case, though that one was less "you're selling piracy tools" and more "you're telling people to go pirate movies". The Grokster case would partially overturn this, so you can get contributory liability for advertising infringing use cases of your software (aka "inducement"), independent of DMCA 1201.
I suspect that if inducement was a valid theory of liability in the 80s, we wouldn't have seen such a huge, cross-industry push to enact DMCA 1201. People selling cracks would be legally liable under the inducement theory, but we wouldn't have a blanket ban on tools that could be used lawfully, like, say, tools that let you defeat parts pairing.
[1] This, oddly enough, had to be proven in court with cases about garage door openers and printer cartridges, which took almost a decade to resolve.
[2] The original law did codify existing DRM schemes (notably Macrovision, which it spends whole pages defining), but none of those are relevant today.