Because consumers don't understand
diffracton and false magnification but do understand a bigger number. Too bad this is only going to make the red amplification problem worse as at a pixel size of 800nm it is getting awfully close to the long range of visible red so it will capture even less of that. I would be willing to be I can capture a better quality image with my old K-2000 (10 year old 10MP DLSR) and old screw mount 8 element SMC Takumar f/1.4 but if I used my K-3 and my modern good glass (I own the 3 princesses) I would absolutely crush it. I'd even be willing to bet I could do better than this sensor with a roll of Ektar100 in my Spotmatic F using that same 50mm f/1.4 lens although it would have more noise from the grain.
That said Sony does make some damn fine sensors but no one who knows about optics and sensors really expects this to compete with even entry level DSLRs or mirror-less interchangeable lens cameras, let alone those monster digital medium formats from Hasselblad or Pentax. Instead it will be something for consumers to get into a phone pissing contest over and believe that they can take pictures just as good as a pro can.