ADB connection problems on LG Optimus Zone 2 running KitKat
Rebooting the phone and setting it to connect via USB as Internet Connection -> Ethernet worked for me.

LG also has drivers on their site (http://www.lg.com/us/support-mobile/lg-VS415PP) but I'm not sure they're necessary for this to work, and even with them installed ADB only works when in Ethernet mode.

You're not wrong to be frustrated, though - I've been developing for Android since 2009 and have used dozens of devices, and I've never once had one that required a setting like that for ADB to work (at least not any Google-certified official devices). Weird.

EDIT (Aug 25 2014) - Looks like after the phone is rebooted or unplugged, sometimes it "forgets" its connection mode, or tries to connect as an installer even though it's still set to do an Ethernet internet connection. Re-selecting the statusbar notification and setting it back to internet+ethernet again works, but it's kind of annoying to do regularly. Then again, for the $25 I spent on this phone, I suppose I can't expect too much...