If you want a girl with a booty but you can’t handle a little tummy then you can get right the fuck outta my face
There is a difference! One is on your face, and the other comes with a massively bad reputation because our culture is terrified of sex and any of its potential consequences aside from babies born to married couples who make enough money that they never have to ask for help. The difference is the stigma that comes with genital herpes, or any STD, and that stigma is far more harmful to the people diagnosed with HSV than is the condition itself. The CDC doesn’t recommend regular screening for HSV in sexually active persons unless they have symptoms, because knowing you have it can cause adverse psychological effects that are more harmful than having it and being oblivious to it, even thought that ignorance means the person in question may unknowingly expose other people.
Nobody differentiated between oral and genital herpes until the 1960’s. The stigma surrounding genital herpes was manufactured by major pharmaceutical companies in the 1970’s and 1980’s, because nobody was buying their anti-viral medications. They had to make the condition shameful before people would buy products to deal with it, the same way they made it shameful people to sweat or smell like they do (so they’d buy antiperspirant) or have body hair (so they’d buy razors). It’s also worth noting that one person’s oral herpes can be spread to another person’s genitals through oral sex, so all your friend really needs to do to give somebody this enormously different condition is go down on them.
Short answer: the enormous difference comes from insisting that there is one.