This can't be directly enforced. You can't make laws for what people to "focus" on.
Though there is a way to indirectly push this notion: Restrict all stock ownership to be a minimum of 10 years. This indirectly puts more focus on dividends.
It also puts more focus on the core misalignment you're alluding at but failed to see explicitly: The misalignment between short term gains and long term gains.
In the end whether private or public they care about profit over customer. But private owners tend to care about customers because customers represent an overall bigger gain in the longer term and private owners are playing the long game.
If all stocks had a minimum 10 year ownership requirement it will change all corporations to focus on long term gains. I believe this one change can fundamentally fix the problem we have with corporations.
Maybe we can test this.
The other thing that needs to be changed is public responsibility. If a company dumps illegal nuclear waste in some river, directly ask for minimum fines from all shared holders. First divide the fine by the shareholder amount, charge each shareholder. Then if it's below a 500 dollar minimum add the remaining amount to get it up to 500.
Pissed off share holders paying 500 will definitely get corporations to stop doing random crap. Maybe even funnel jail time to board members or C-level execs. If a corporation is responsible for deaths it's justice to place actual people responsible rather then giving "jail time" to a corporate entity that doesn't actually exist.