Why does El Capitan keep resizing my Finder window?

It's a bug. Report it to Apple:

http://www.apple.com/feedback/

I'm not sure if this is related, but my finder window seems to have issues as well ever since upgrading to El Capitan - it frequently will start up (or perhaps it's when it wakes from sleep?) - and the finder is quite small - not the last size it was set to or the default - and when I drag the lower righthand corner out to manually resize it and make it larger, the whole finder jumps suddenly over while being resized (resizing still happens, but not as intended of course). It seems particularly prevalent when the finder is sitting in the upper lefthand quadrant of the screen.

I've seen similar behavior occasionally in previous versions of OS X too on Mac Pros working with external displays (non-Apple ones). It was too rare to be a problem for me.

I just got a new iMac with El Capitan pre installed. My finder windows do not remember being resized. And icon placement is flakey also. Open a window, resize it then close and reopen and it's back to it's original size. Not like any Mac OS before it. I've had a Mac since the Mac Plus came out so I'm familiar with how it's supposed to work. Irritating