Author List of Gravitational Wave Paper

They should let Yoko Ono sort it out.

Although she’s experienced, I can’t vouch for her success rate.

The American Mathematical Society doesn’t characterize the tendency as quite that extreme. According to their 2004 “culture statement” on publication of joint research, alphabetical order is used for 75% of jointly authored mathematics papers. (For pure mathematics, it’s a much higher 90%, which better fits your “virtually always” descriptor.)