Your second line is simply not true. Both American [1] and United [2] have committed to waiving change fees if you don't want to fly on a 737 MAX. Southwest is farther away from bringing the MAX back into service, so they have less detail on their site [3], but it sounds like they'll do something similar.
The CFM 56 on the 737 (NG or Classic) also has a flat bottom. E.g., [1] shows a 737-800 with an engine with a flat bottom, and [2] shows a 737-300 with an engine with a flat bottom.
It's fairly common in antitrust. Section 16 of the Clayton Act [1] gives states power to bring federal antitrust suits on behalf of their residents, and states will often bring both federal antitrust claims and state antitrust/unfair and deceptive trade practices claims in the same suit, as the states here are doing. Incidentally, if you're interested in the surprisingly expansive role of state attorneys general, the National Association of Attorneys General has published a fascinating (though pricy) book that goes into the common powers of state AGs in more detail than anybody would want.[2] The website for James Tierney's State AGs course at Columbia also has a lot of interesting readings.[3]
Yeah, I laughed when I read that sentence. Although some rules in law have naming conventions that tell you something about the underlying rule (for example, the merger doctrine, or assault with a deadly weapon), a huge number of rules are named after the case that created the rule--or, in other words, just a person or company's name. So in administrative law, you might apply Chevron deference, or say that a post-hoc rationalization poses a Chenery problem. And, of course, sometimes lawyers disagree about what case created or recognized a rule, so you'll have some people calling something Auer deference, with others calling it Seminole Rock deference.
Not a lawyer, but have worked with lawyers in a law firm and government offices. Everywhere I worked did almost all legal work in letter format. I occasionally saw legal paper, but no more commonly than in non-law offices.
[1] https://www.aa.com/i18n/travel-info/737-MAX-return-to-servic...
[2] https://www.united.com/ual/en/us/fly/travel/inflight/aircraf... (under "What if I don't want to fly on a MAX?")
[3] https://www.southwest.com/737-max/#return-to-service-plan (under "What are Customers' options if they don't want to fly on a 737 MAX?")