You can configure some IRC servers to mask all IPs by default, for instance the Ergo IRCv3 server does so automatically: https://github.com/ergochat/ergo/blob/master/docs/MANUAL.md#...
The fact that server operators of many (all?) networks refuse to enable cloaking by default just shows that IRC has a very different culture than what modern users have come to expect.
In my mind there is no reason for cloaking to not be enabled other than "it's always been that way and I like seeing ISP hostnames when people join!".