ESG is a political compliance score. Fall out of favor with certain groups and your score will plummet, publicly tout an agenda around diversity and sustainability and your score will rise. The fact that Exxon (edit: oops I mean shell) has a higher ESG score than Tesla should be all you need to know.
As I understand it ESG rankings are generally done relative to other companies in a market segment. They aren't saying "this airline has a high ESG score, they must be less environmentally damaging than this farming company with a lower ESG score". They're ranking which airlines do the "good" things (for some value of good).