Boeing, like many B2B companies, is B2B2C. They may not sell directly to the public, but they have a public brand. (Unlike Spirit AeroSystems.) And therefore,

Boeing, like many B2B companies, is B2B2C. They may not sell directly to the public, but they have a public brand. (Unlike Spirit AeroSystems.) And therefore, B2B companies run ads, e.g. to sway public opinion on government policies, or (now) to restore flyer confidence in their product. If US airlines get enough emails and letters from customers saying "I'll never fly a 737 MAX again!", that gives the airlines huge negotiating leverage against Boeing.