Why does the battery saver not re-enable WiFi after a full charge?

Sometimes I forget to charge the phone and it goes into battery saver which as you know disables certain features that would otherwise use battery such as WiFi, but recently I found that after I charge the phone the WiFi doesn't come back on again, and I have been using phone data all this time,...

Why does the battery saver not re-enable WiFi after a full charge?