There is a caveat, though. Like many older protocols (ftp) there is a lot that was not initially written down or left up to clients and server implementations. This, does lead to a lot of edge cases you need to be aware of once you want to actually support a wider user group.
Also, as this is apparently is still a discussion. IRC is not simple from a modern user UX perception. Registration can be complex and confusing, though hidden a bit through clients. Managing channels with various flags is a whole other thing. Then there is also the fact that these days people are no longer used to the fact that they can't see messages from periods where they were not connected. Of course, the latter can be easily handled by a BNC or fancy clients like https://thelounge.chat . But, that is only easy for technically inclined folks.