how can someone be as driven and hard working as chris christie and stacy abrams while being overly obese??

Many political figures are "larger than life" literally and figuratively.  Quite often, their size is a reflection of that appetite for power and influence.

I lived in the DC area back in the 1990s and a good friend of mine was a beltway journalist that got me access to a lot of the old time pubs and grills popular with the political set.  Some of the old bartenders told me about how Tip O'Neil and Teddy Kennedy would order three entrees each over the course of a four-hour dinner.  The kitchen that serves the private Senate dining room apparently has a walk-in freezer just to meet the members' demands for ice cream.

New Jersey politics still has an "old school" feel to it, and if you study the history of powerful political bosses (and crime figures) you'll find no shortage of big men.

For Abrams, would she have the same presence in your mind if she were a petite woman?  Note how the ones with traditionally good looks like Michelle Obama and Kamala Harris tend to rise up through the ranks in secondary roles and through associations... it's the snarky (Rice) and outspoken (Waters) that make it on their own.

Thyroid trouble or diabetes can play hell with your weight. 

Everyone has obstacles and difficulties and shortcomings in life. For some people, those faults are just outwardly visible.