The reason for not wearing underwear is that it can cause chafing or pressure points where it shifts or creases. Cycling shorts are designed to minimise that by not doing either. There is nothing nasty about cycling shorts if you wash them after each ride. If anything they handle sweat better than cotton underwear would.
That being said, if you feel better wearing underwear, then you should feel free to do so. But there are practical reasons why most people don’t and they don’t have anything to do with trying to be a “real cyclist”.
The reason for not wearing underwear is that it can cause chafing or pressure points where it shifts or creases. Cycling shorts are designed to minimise that by not doing either. There is nothing nasty about cycling shorts if you wash them after each ride. If anything they handle sweat better than cotton underwear would.
That being said, if you feel better wearing underwear, then you should feel free to do so. But there are practical reasons why most people don’t and they don’t have anything to do with trying to be a “real cyclist”.