>>374240847
some people who had a previous generation of VR headset (HTC Vive), those also came with 'lighthouses' 1.0. so if you already have 1.0 lighthouses and you wanted just the index, you can buy a kit without lighthouses. 

another reason is maybe warranty related, if your index 2.0 lighthouses still work but your headset/controllers are like 2+ years out of warranty and broke. 

or maybe even people who just want multiple headsets in the same playspace for some reason, or backup headset.