DBus actually uses unix sockets (though I believe it can make use of other transports as well). If you're going to use a raw unix socket, you have to design your own RPC mechanism over it. For some things, that may not be a big deal, and may be preferable to pulling in a dependency like DBus. But for other things, not having to do that work might be a win.
DBus also allows for fine-grained permissions that you can't get with unix sockets without designing and building that mechanism yourself.
DBus actually uses unix sockets (though I believe it can make use of other transports as well). If you're going to use a raw unix socket, you have to design your own RPC mechanism over it. For some things, that may not be a big deal, and may be preferable to pulling in a dependency like DBus. But for other things, not having to do that work might be a win.
DBus also allows for fine-grained permissions that you can't get with unix sockets without designing and building that mechanism yourself.