... and IFTTT, Tasker, and any number of of automation apps that require the user to both be aware of and be bothered to set up correctly.

Developer preview 3 of Android O includes a great option in WiFi settings to automatically turn WiFi back on when you are in a location where you've connected to a 'high quality' WiFi network before (such as home or work), though I've not dug deep enough to find out what constitutes high quality, and it doesn't appear to be paired with a converse option to turn it off elsewhere.