Bouncers and log bots have been a thing even 20 years ago when I was active on Freenode. In fact, a bouncer and log bot was what made me get my very first own VPS... time flies. It lasted a year until my first attempt at a libc upgrade failed, that was a lot of work to fix.
Being able to get a text file log dump easily is also light years ahead of what most people are able to do on discord.
In order to get log bots or bouncers up and running it required some technical know how (meaning most people didn't do it, thus staying ephemeral as default) but those that did do it were well aware how to get and export those log files for archiving etc (thus why we have things like bash.org).
On Discord it's default and while yes someone could setup bots or something to export some of the content - that requires some technical know how (meaning most people won't do it). Thus everything in there goes away when the service closes.... even though the DEFAULT EXPECTATION is that information there is forever.
Discord on the other hand does everything IRC does but people have made it take the place of forums, blogs, file repos, etc etc. All this information is locked up in a platform that can't be searched or often even accessed without signing up for the platform. Unlike IRC however Discord is not a protocol that others can tie into - it's a platform and they can/do actively lock people out of it.