I had my four babies in the 70s and 80s. All had their naps in the garden but they weren't abandoned at the bottom of the garden, unseen and unheard. They were in a safe back garden, near the kitchen window.
Prams were robust and weatherproof - if it was misty or driving rain/snow, my babies slept indoors but for those who asked whether parents would choose to sleep outside in cold weather...er, yes please, as long as warm clothing and a huge pram were available.
Mine wore woollen clothes in winter, and slept under woollen blankets. The hood kept draughts away, but they were still getting fresh air (I suppose that might depend on where you live!). Modern baby clothing is mostly cotton, which isn't warm - in winter, wool is probably better.
In summer, the hood would be down, sun canopy in place, and the pram would be put into the shade. We had cat nets, though I only used them when I was worried about wasps. When the baby woke from a nap, you'd see the pram start to bounce gently - I think that was a lovely way to waken up, outside, under a tree.
I'm wondering whether those babies who don't sleep outside are ever allowed to be out when it's cold? Do they spend all day inside the house or car? That sounds very unhealthy to me.
And yes, the latest thing is forest or outdoor nurseries - up here in Scotland that will mean playing outside in low temperatures for much of the year - is that a no-no too?