Useless Automatic Quick Scans vs. Fruitful Manual Full Scans

Greetings,

I've been a Windows person for almost 3 years now. In Appleland I never had to sweat virus activity. In Windowsland I've had to explore how and where people get viruses. (Morbid curiosity.) I now know the type of dicey sites that infect, but something about Windows Defender confuses me something silly.

Defender runs Quick Scans all the time. I think only once in 3 years has Defender found anything that way. However, when I run a FULL scan -- that's typically when stuff is found.

If my question isn't obvious at this point it goes a little something like this: why doesn't Defender run full scans more often?

Also, I once got the same virus in the same place. (Chrome has a hole in it apparently where Firefox Quantum is more secure.) Anyway, if Defender found something in one place once -- why doesn't it automatically add that location to the quick scan?

It's so very strange. It's like Defender doesn't care to find virus activity.