At some point they should be done with all the market research there is to do and either go big or stop wasting resources on building gadgets for it.
Freshdirect is NYC area and Philly, Peapod has a few markets but they are part of a grocery chain so everything but the last mile is take care of logistics wise. It seems like figuring out how to do it at scale and be competitive is exactly what Amazon is doing. If they can make it almost as cheap but have compelling additional features then it helps them roll it out wider.
With their main business they chose to grow as fast as possible and are still figuring out profitability. When you're selling electronics with 50% markup that works. Groceries, which have <5% margins, not so much.