The main reason that asymmetric (RSA, eliptic curves) encryption are broken (on quantum computers) is simply due to relying on certain assumptions that haven't

The main reason that asymmetric (RSA, eliptic curves) encryption are broken (on quantum computers) is simply due to relying on certain assumptions that haven't been fully proven (and instead has been disproven over time). Symmetric and one-way functions are provably secure, within those characteristics that they define. Notably, they are not designed with "until the end of the universe" promise (and the only proven "until the end of the universe" encryption anyway is a proper one-time pad (or disk) encryption). The reason that certain hashing and encryption algorithms have been broken are due to both compromises inherent in design goals (notably, AES have been simplified from the reference encryption Rjindael to ease up hardware acceleration) and the march of technology simply rolling with faster chips. Quantum computing can speedup this process a bit (a quadratic speedup in most cases), but not enough to outbeat these types of encryption.