Delivery players like DoorDash ( DASH ) and Instacart's parent, Maplebear ( CART ), fell 4% and 11%, respectively, and dropped again on Thursday. Meanwhile, Amazon's stock has gained 3.5% since the announcement. JPMorgan said Amazon's grocery blitz could significantly widen its lead in US e-commerce. The strategy may build strong Prime appeal, drive higher purchase frequency, increase ad revenue, and pressure legacy grocers to rethink pricing and delivery fees. The firm notes that Amazon has been cutting costs by building out same-day facilities, placing inventory closer to customers, and deploying more robotics and automation. These efficiencies, combined with Amazon's pricing and scale advantages, could allow the company to grow its grocery business without the profit drag typically associated with fresh food delivery. More grocery customers also means more opportunities for Amazon to sell ads — a business that grew 22% year over year in Q2.