If IRC were designed today, it would probably be with E2EE. But it's not the end of the world that it wasn't, it just limits what use-cases it's appropriate for. Asking about kernel config options in #linux does not really demand particularly high privacy, and TLS between you and the server is generally sufficient. E2EE is also pretty difficult to get right and dramatically increases the complexity of the system -- Matrix's third-party client ecosystem is hamstrung by this requirement and very poor compared to IRC as a result. E2EE is nice to have and essential for some use-cases, but I don't think that IRC is invalid because it lacks it.