People like niceness, fluffiness, prettiness, and fun. People like people who make them feel good about themselves, and the twins were masters at that. They liked everyone and made everyone feel like a friend. They were literally bundles of joy, and had highly evolved social skills and never got mad at other people or made them feel sad. Even Brian got dumped in the genuinely nicest possible way. They're just so sweet - what's not to like? Why should they be disliked just because they don't do debates?
People respect brains when it's directed at something creative and constructive, and those who don't have brains wish they had them for themselves, but generally dislike other people who don't know how to hide them because they feel unequal around someone smart (they perceive smarter people as having some kind of inborn privilage, so are less likely to be kind to them and to support them) - especially if they have slightly depressive, cynical, or critical tendencies (and most smart people are somewhat miserable). Ever heard "the nail that sticks up highest is the first to get knocked down"?
Liam was a smart lad, and he was also smart enough to keep that under wraps. Gerry and Jonty may have been knowledgable, but their social skills were certainly less evolved than the Twins, Liam, and even Brian.