Mens sizes have changed over time. Go get a vintage t-shirt from the 80s, medium size, and try it on. It'll be the size of a small or xs today.
you're right! i just try the clothes i used to wear as a toddler, it's ridiculous how much they don't fit
it's not always necessarily about people being fat but also about style, tighter t-shirts where more in fashion back in 70/80s, not it's more loose style
I meant more the pants and dress shirts, which are sized in inches.