How come employers can't blacklist these badly behaving employees who don't give any notice before they quit? Because government regulations only allows past e

How come employers can't blacklist these badly behaving employees who don't give any notice before they quit? Because government regulations only allows past employers to verify that 1) yes the employee worked here 2) this was his job title and 3) these are the date ranges when he worked. Telling anything about "was he a good employee or not" is grounds for a lawsuit. That has removed incentives for employees to give notice before they quit.