So if we look at this patent application the why has been unanswered (up to this point in time).
https://image-ppubs.uspto.gov/dirsearch-public/print/downloadPdf/20240004147
In my opinion this approach would provide an efficient means to couple multiple VCSEL outputs at different wavelengths into a common waveguide for fiber transmission.
https://agoracom.com/ir/POETTechnologies/forums/discussion/topics/797553-patent-application/messages/2402857#message