They have social anxiety because they never went outside. “Outside” and “with other people” are our ancestral environment. Social media is abnormal and makes abnormal people.
I have social anxiety because of a lifetime of psychological and physical abuse from everyone I have ever considered “family”, with only two exceptions. It has nothing to do with “outside”, and your idiotic hot take discounts the lives and experiences of thousands who have been through similar situations and worse.
It discounts no such thing. Your unfortunate experience (for which I truly feel sympathy) has nothing to do with how evolution or socio-biology work or the significance of our ancestral environments or the statistically significant fact that even you, with your unique and very real burdens, if you went outside and met with other people would probably feel less anxiety.
"with other people" means family group. Society changed radically once the Industrial Revolution hit and people started living in environments where they didn't know well everyone around them.
In a non automobile culture you absolutely did know the people around you, Industrial Age or not. And if you think the people around you being family would somehow make it easier, I think you need a little more family. :)