Was it ever realistic to assume that teenagers, college students, and other young people were going to stay at home and do nothing for spring break or during the summer? Of course not. For better or worse, Americans in particular have a unique penchant for rejecting authority, which is why lockdown efforts failed spectacularly in the United States. We can’t even get adults to wear masks.
Now, that doesn’t mean that lockdowns don’t work anywhere. Just like abstinence-only sex education, some people really do follow the advice. Strict lockdowns largely worked throughout Europe and Asia, for instance. For better or worse, Europeans and Asians tend to be more compliant and community-minded than Americans, which is one reason why they may be more willing to submit to restrictions. (However, my guess is that they would not follow them indefinitely.)
The point is that successful policies must take biological reality and culture into account. What works in one country (or even most other countries) may not work in another one. Spain isn’t about to ban the running of the bulls even though it’s incredibly stupid and people have died.