They are massive scams designed to sell products and generate income for professionally run charities. Experienced runners usually avoid them because they are over priced and packed with overweight slobs who didn't do the training but want their co-workers to be call them an athlete.

Literally anybody can do a half marathon. Waiters, mailmen, etc all pull those distances every shift.

Telling people you ran a half marathon in a substandard time and thinking that makes you "disciplined" is like walking across hot coals at a $3000 Tony Robbins seminar and thinking people will be impressed. Stupid people will be.