Why did he sell the Airlines?

Said, I think Buffett sold the airlines because the operating environment and outlook for the airlines suddenly became much worse and much less predictable due to COVID-19. There's also been speculation that, given the airlines' need for a government bailout to survive the worst of the pandemic, Buffett recognized that Berkshire's substantial ownership stakes in the airlines could impede that process, thereby imperiling their survival (because what politician wants to be seen as having bailed out Warren Buffett?). In other words, the airlines might have done worse if Berkshire had kept its ownership stakes.

I don't view these as "macro" calls in the sense of, for example, making predictions about the U.S. or global economy or about what interest rates might do in the next few months or years. Instead, they are very sector- and company-specific reasons for selling the airlines.

When Buffett says to ignore the macro, I don't think he means to ignore the knowable operating environment and impact on demand for a company's products or services. And the knowable operating environment at the time included a pandemic that shut down the airlines and would significantly reduce the demand for airline travel for an unknown period of time. How things would play out for the airlines was very unpredictable. I suspect Buffett thought either that the airlines were no longer a good investment because their prospects for the reasonably foreseeable future were severely impaired, or that they belonged on the "too hard" pile.