This quite informative answer to a Stackoverflow question (via) answers the question, or at least provides a great deal of context that I didn't know. It turns out that the reason AT&T syntax puts the destination register second (instead of first, the way Intel syntax does) almost certainly stretches all the way back to how PDP-11s encoded instructions.

(The AT&T assembly syntax, commonly used on Unix systems but not uncommonly disliked (via), is a cross-platform general syntax that AT&T and Unix mostly used on a range of platforms. The specific x86 version of AT&T syntax is yet another adaptation of this general syntax. More information on the difference between AT&T and Intel syntax for x86 can be found on, eg, Wikipedia.)