I think the issue with shipping is taking an (hopefully) 8 wk old puppy away from its mom and everything it’s known and sticking it in a crate to be shipped, alone, with lots of terrifying sights and sounds and bumps and bangs in the cargo hold of an airplane, which can have extremes of temperatures and frequently lose pets, etc. I think a pp was implying that many good breeders won’t subject their beloved puppies to this sort of thing. Many say NO SHIPPING on their websites. Though I’m sure some can be found that do, too. I’ve read about dogs over the years having fear issues related to noises which could possibly be traced back to an experience like this during such a critical time of development.
OTOH, having someone fly with them in the passenger area of a plane isn’t a lot different than someone leaving in a car with a puppy. For a short time they’ll be comfortable with a stranger who will assure their well-being, until they meet their forever family when they land.
So I think there is a difference.
I worked with rescues recently who required I drive to distant states because they did not allow shipping, either. (And I was willing to do it for the right dog.)