Why do some people choose to buy underwear online?

Have you ever had such an experience:When you go to the store alone,a male staff will check your breasts and advise you to wear a bra, it will inevitably be a bit embarrassing. Plus when there are other male customers out there, the situation becomes uncomfortable because we can't really talk much about the kind of bra we want. Its always better when there's a lady at the shop so you can explain to her your girl issues with bras and she'll suggest you the type of bra that might help, but with male staff at the stores, we can't be very open.