as you can see, that's because people still use MSN!
kidding.
first, there was MSN. then, lots of programs have integrated with it, so that they could make it display the track you were listening to (most of them, but not all, were music players).
then, there were other programs that have been mimicking MSN in order to receive such events: say, you wanted to type /np in your friends' IRC channel somewhere on Rizon and have it reflect the actual "then playing" track, or do something else based on the audio that's been on -- you'd like your IRC client to be aware of it.
for instance, when Sieg has made his
Modding Assistant, I've added a MSN-like integration, making it pose as MSN, so that a modder running it could say "I want to mod what's currently playing in osu!", and click the button, and go to the current song's directory. besides, a couple of streaming companion tools, like
that of Piotrekol, rely on the same mechanism to show the track on Twitch overlay.
now, if you remove that functionality from osu!, you'll leave a portion of software clueless of what is currently playing, thus breaking backwards compatibility. of course, if you have a heart like that of Macos developers, who have fucked millions of people at the same time by releasing OS X Catalina without 32-bit applications support, you'll go for it.