but for brick-and-mortar restaurants, clothing, and electronics stores to have only Zuckpages struck me as bogus,
Those who wish to serve the general public with a website need to find another platform.
I agree, I don't think Facebook was designed to be a commercial or organizational web site, especially with e-commerce seemingly being so important, I don't think payments can be processed on Facebook. It is mostly a place for family, friends, acquaintances, and people with mutual interests to interact and share information and pictures. I suspect some businesses use Facebook in lieu of a web site because they probable aren't "web savvy" and / or don't want to pay someone to build and host a commercial web site ... Facebook is no-cost to them. Some may use Facebook as a way to direct traffic to their commercial website ... I've had web search results where a business or organization's Facebook shows up but not a web site, but if they also have a web site the URL will likely be listed on their Facebook.
Another reason a business or organization might use Facebook is for it's "push factor" (if I'm using the right phrase). My regional library had both a web site and a Facebook. As I "follow" their Facebook I get notifications of upcoming holiday closures (and weather closures) and special events "pushed" to me when I open Facebook. I otherwise may not know about these unless I had seen flyers at a library branch or checked their website daily, which isn't practical. The same thing can be done by joining e-mail or text message lists, but I don't want those communication pipelines jammed up with notifications, I find Facebook better suited for that kind of information.
I suppose it comes down to a situation of (1) If Facebook has information or communication features that one finds useful to them, they will have an account so as to take advantage of those features ... or ... (2) If they don't find it useful, or don't like how it operates, then just don't use it ... the information and communications features exist in other venues and by other means.
But Facebook is definitely NOT dead.