You forgot the biggest drawback to employers: not being able to get honest feedback about the prospective employee from the previous employer.

It's a noisy signal.

Some employers still answer a binary question "Eligible to re-hire? Yes/no" and that tells a lot in one bit of information. Of course some employers are vindictive and they just say no out of spite. Others will not answer anything except confirm dates of employment. Or they provide a good reference on a bad employee just so they leave without having to fire them.