Based on my own childhood in Minnesota with “old school parents”, versus what I see in the Bay Area with my current parental peers:
Because, by and large, we massively over-dress our children.
Children may not be fully aware of their bodies, core temperatures, or potential for catching colds, etc… But in my experience, you put five or six of them together on a playground, there’s no amount of clothing that will prevent transmittal of all kinds of bugs.
Further, when kids say that a jacket is “too hot”, they may actually be on to something – as the querent said, their higher metabolisms do quite nicely in temps that most Californian adults would consider unlivable outside of Tahoe… And that most midwesterners would call “shorts weather” in springtime, with snow still on the ground.
Finally, based solely on my own experience: kids want to have more personal control – and when my 3 year old daughter insists that it’s not cold out (having stepped outside into the sun to test, but between strong gusts of wind), I have learned to respect her opinion, so that when her teeth are chattering a bit on the swings at the park, she’ll remember to at least put her windbreaker in the snack/water bag she carries when she doesn’t want to wear it all the way there and back. When I have the patience myself for such lessons, they are by and large learned after only one or two instances… But when we “baby her” as far as the weather goes, or always seem to have those rain boots or socks or knit beanie at the ready while out and about, she takes advantage and revels in the personal butler service entirely knowingly.
When your kid can verbalize their own intentions, expectations, and desires, try listening more to them, and accommodating or negotiating where possible. Amazing things can happen – I have a 3 year old who takes her own showers, fully dresses/undresses herself, and can produce her own non-cooked meals safely and with small enough mess it’s totally worth the free time I get back. Compared to her peers, she seems lightyears ahead, but it really all comes back to listening to her, and treating her reasonable suggestions and plans as reasonable.
In summary, I’d say it’s a combination: higher metabolism and core temperature, an accompanying misperception of such on the part of parents/adult caregivers, and resistance against imposed rules/yearning for greater independence.
This answer originally appeared on Quora: