Maybe they understood from the beginning that the only way she'd get what she wanted was to attach herself to somebody with people skills, and the only way he wouldn't go off the rails was to have someone to crack the whip.
A lot of idiots nostalgic for the 90's, if only because they were 25 years younger then, would be receptive to Bill and his old pig.
All this depends, of course on the Clintons' health - his more than hers.