Dollar cost. I'd love to switch away from beef burgers for a health and ethical reason, but can't justify a $15 burger when most burgers at a nice restaurant are $10 where I live.
Two 1/4 lb. frozen patties are around $6. I've never been a fan of veggie burgers, but these really do taste excellent and the nutrition profile is great.
I think the patties were sold in pairs at Whole Foods for about $8, so $4 a piece. Kind of steep but in a world where people pay $9 a serving for BlueApron seems competitive enough.