I take my shoes off at the airport response to an attack that happened 20 years ago with 3,000 fatalities, and this dude on the bus won't wear a mask to help stop a disease that killed 10,000 people yesterday.
Ultimately, the events of 9/11/01 were entirely predictable — in fact they WERE predicted — as an almost natural response to the behavior of the United States domination and sponsorship of atrocity, worldwide. The attacks with airliners were spectacular in a visual sense, but microscopic next to the United States' casual commission of atrocities, from year-to-year —Before the events of that day and as accelerated since then.
A return of those tactics has not been because of US success in a military mission of suppression and disruption of "terrorist" networks. In fact, both directly and through proxy agency, the US has funded and equipped more armed radical militia than ever before - dwarfing efforts with Mujaheddin groups in the 1980's.
Rather, 9/11 was insignificant and ineffectual as a tactic. An overblown bloody-nose, delivered at great effort and waste of expense, largely produced by the delusions of Osama Bin Laden, who became nearly abandoned by Jihadist/Salafi movements, almost immediately.
Anyway, happy 20th birthday, USA. Couldn't happen to a nicer bunch of folks.