I'm curious, many comments here mention all the legal and regulatory permissions-based aspects of getting into the HAM radio network, but what is it, practicall

I'm curious, many comments here mention all the legal and regulatory permissions-based aspects of getting into the HAM radio network, but what is it, practically, that stops any young person from just buying the right equipment and starting with transmissions on their own? Does anyone even seriously enforce this? Why is it so regulated in the first place if its just partly amateur hobby radio of a sort? Asking as a someone who knows very little about HAM.