"The simplest answer is that we tend to favor groupings of three." Early-born jazz musicians didn't.

http://playing-traditional-jazz.blogspot.com/2014/05/sixteen-bar-tunes-in-traditional-jazz.html

http://playing-traditional-jazz.blogspot.com/2014/04/how-to-play-traditional-jazz-do-it.html

Handy described 16-bar strains as "conventional," and recalled that his would-be publishers of blues (as of roughly 1911) complained to him that a 12-bar strain sounded incomplete. That's because as jazz grew out of ragtime, 16-bar strains a la Joplin continued to be routinely used.

That's 16-bar strains in general I'm talking about, not normal 16-bar blues in particular, such as "One Dime Blues" by Lemon. For instance, "Do What Ory Say" has a repetitive chord progression, is 16-bar, and is not a blues.