My health insurance--various over the decades--has never covered mom & pop pharmacies, only big chains, just like not every doctor is in-network...
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This might be a mis-perception on your part (depending upon what you mean by "over the decades") The large scale cost-cutting and low price bidding strategies of both pharmacies and health care providers is something of a comparatively recent phenom. If you were prescribed a "very expensive antibiotic" as a dispense as written presciption, it's highly unlikely that you could've gotten it at Sam's Club or wherever for $10 for a 90-day supply.

That particular incident occurred in 1994. The insurer refused to cover this drug at all becasue I was "out of network" at a Mom & Pop pharmacy. That's when I learned that health insurers have deals with pharmacy chains. When I expressed my surprise to people I knew, they were surprised I didn't know that already. sigh.

Alas, I don't seem to need drugs that cost $10 for 90 days or anything like it. My current insurance has me paying $50/month for the only drug I take (Nasonex, steroid nasal spray for allergies)--$40/month mail order, but I need to read this year's policy, which I haven't done yet. (Yes, I've tried generics & other cheaper versions, but they don't seem to work for me--a couple of them actually stuffed me up worse! So I've been taking the Nasonex every other night for the past year or so, and am trying to get to twice a week now...depending on the allergen load in the air, may or may not work any particular week.)

ASIDE
No, it isn't very good insurance--it's watered-down BCBS for state employees...for some reason <Fox News, I imagine-> people assume that every government employee everywhere gets a great benefit package like big unions in big cities do. Nuh-uh. At least with the ACA, the low lifetime limit was wiped out. Let's hope Congress doesn't turn that back.