I could see a policy where YouTube made Unlisted videos Private that only had referrers from social media; this would be a welcome compromise to ensure non-guessability of URLs. But I can also see how this could become complicated and political. And companies using YouTube in this way aren't really contributing to YouTube's revenue materially, so there's not much incentive relative to the reputational risk of people guessing Unlisted links.
I shudder to think that healthcare professionals or heavy-machinery operators might be relying on these links to be trained in systems they use, will start to see broken links, will never report them back to the right people at their system providers, will just not get the full training, will make mistakes, and might cause harm as a result.
Security is not the only component of safety, and impacts need to be evaluated holistically.