The Bukit Chagar Luxurious Apartment is one of the earlier high-rise establishment where there were still "Apartment" terms in play. Facilities wise hands down the newer Tri & Twin Tower wins by miles ahead and this drives demand and the equation here is demand = price.

Furthermore the old apartment tends to have a bigger layout hence what the owners do is they partition it to have more room to rent it out, vs a more modern layout with limited capabilities of partitioning, and that drives up the room rental price even higher.

Last one I think would be the most crucial one as well, is the distance to CIQ. Tri-Tower > Twin Tower > Bukit Chagar Luxurious Apartment. The distrance may not seem to be a huge difference by driving, but when you try to walk it does certainly requires extra effort especially its an uphill road towards the apartment. Not to mention in the safety perspective as well. I'm not sure the condition of the road after reworked, but back then the road there was horribly eerie and dark during night time. Easy for nasty things to happen.