One issue is a lot of people have mobile devices as their main method of interaction rather than desktop computers and it is hard to maintain the continuous connection required by a MUCK. It doesn't need to use an notifications system but it does need to be able to handle being unable to send or receive for a bit and catching up later.
In theory TCP can do this, but for various technical reasons it often does not/is forcibly disconnected by intermediaries, so modern chat systems tend to have a replayable message-oriented protocol at a higher level where you can request all messages from time X, rather than just pushing the output onto the network and hoping for the best.
One issue is a lot of people have mobile devices as their main method of interaction rather than desktop computers and it is hard to maintain the continuous connection required by a MUCK. It doesn't need to use an notifications system but it does need to be able to handle being unable to send or receive for a bit and catching up later.
In theory TCP can do this, but for various technical reasons it often does not/is forcibly disconnected by intermediaries, so modern chat systems tend to have a replayable message-oriented protocol at a higher level where you can request all messages from time X, rather than just pushing the output onto the network and hoping for the best.