Is there a specific reason why only this one system has the description and not all 4 of them? Imho it would make sense to put the description on all of them.
I'm not part of the GMP team, but likely it's to not clutter the map unnecessarily, and for general convenience. In this case (and in some others this has been done too), closely related and close-by POIs are integrated into one. For example, V945 Scorpii's POI description mentions various nearby related systems that can be of interest to the visitor, instead of having an individual GMP enrty for each of them. Some others, like Shapley 1, include in their descriptions nearby expedition waypoints or similar things. Bleae Aescs ZE-A g4 (Dragon's Head Nebula) has in its description a handful of other related POIs, as in this case the nebula encompasses many systems and this specific one has been selected to stand in for the whole nebula which the description is about. So this kind of thing is common enough.