I believe struct sockaddr was supposed to serve the role for which sockaddr_storage was later invented. That's why it has the padding array sa_data: so that if you actually define or allocate such an object it will be big enough to hold any address. In no way is that a flexible array, and you never want to be accessing it.

Probably, sockaddr_storage was introduced rather than making sockaddr's array bigger because by that time the definition of sockaddr had become a mystical sacred cow, not to be touched. Plus that size of 14 is the same on every system. It is a one size fits all approach which is not a way to define the maximum size structure over all the address types if you want every platform to be able to make it a tight fit. The size is going to vary with implementation due to different alignment and padding requirements.