I am not sold on the 0w20 is better than a 5w20 or a 5w40 is better than a 15w40 thing. While I will agree that they are darn good oils, there is more to it below the surface. A 0w20 will almost always have a higher NOACK (burn off vaporization rate) than a 5w20. Can't be helped. The 0w20 will require more viscosity modifying polymers in the mix. Those modifiers can break down and burn off quicker than base oil itself.
For instance, just a look at Amsoil's spec sheets, just because they are convenient to find and are similar to most other name brand oils. Their Signature 0w20 will have a NOACK of 10, while their 5w20 has a NOACK of 6.3. Again, the lower the number, the better indicating less volatility of the oil.
Their 5w40 has a NOACK of 9.1 while their 15w40 has a NOACK of 6.8. Again, lower number is better.
If one is not having to deal with some real blistering cold, then why use a 0w20 when a 5w20 is actually a better product? Even when I lived near Fairbanks Alaska for 10 years, I never used a 0wXX oil, nor did many of my neighbors. When it gets that cold, we used the gray matter God gave us and had oil pan warmers, block warmers, and battery warmers on our vehicles. Only a fool would let a vehicle sit overnight out in -35F weather and not have it plugged in.
Even today, in my 2006 Caddy and my 2015 Silverado, I use a 10w30 though they both specify a 5w30. Same reasoning as above. I am not dealing with sub zero temps than often, and even then, my vehicles reside in a heated garage when not in use. I do use a 5w40 in my semi truck, during the winter months as it is out and about all winter and not garaged, and then a 15w40 during the warmer months. My CUT has always gotten a 10w30 HDEO, but it also has both block and oil pan warmer plugged in when needed.