I almost always go to CVS when I need to get a few small items in a hurry (I usually use Amazon Fresh for groceries), so I'm not surprised about this at all. Going to CSV is much easier than fighting the crowd at Walmart since there's only a handful of people there at any given time.
Yet, despite the poorer selection and higher prices, the majority of groceries that enter our house come from CVS. Why? My wife visits one regularly to pick up prescriptions, and they have just enough of what we buy, at sufficiently justifiable prices, that she can get enough of what we need without an extra trip to a different store.
The most convenient store is the one you're already at.