Personal responsibility is what you focus on when you are talking to an individual. If you are trying to make your life better, or someone you know's life better, it is great to talk about personal responsibility and making choices for your life.

But that doesn't apply when we are talking about society wide shifts in behavior. It isn't like people suddenly got genetically better or worse at taking personal responsibility. If suddenly a lot fewer people are making healthy decisions, that isn't because we just happened to birth a bunch of people who don't take personal responsibility. Something has changed. Individuals have a lot of control over their own lives, but at a society level all of those individual decisions average out, and you are left with a representation of the effect of society.

Systemic problems require systemic solutions.