I dress for what I see outside/expect, our seasons are nothing like they used to be, all messed up now. I'm like you and wonder why some people have so many layers on on certain days, and why so little on others. Its only this last week that I've regularly worn a t-shirt + another layer outside. Many others seem to dress in a certain way because its a certain month.Is 70 deg F/21 deg C today. Which, in isolation, is lovely, actually perfect maybe. The next 3 days with be close to 20 deg F above normal.
Do you dress for the season or for the weather? I live in a densely populated area so there were many people out and about. Except for 2 people I spotted wearing T shirts like me, everyone else (except for those in traditional Orthodox Jewish attire) was wearing a coat or jacket. How could they stand it?