The one and only reason I am considering office depot as a place to spend my money is because they're local and I can go get whatever cable or thing I need, right now.
A. [explicit claim; humorous] Analytics confirm that, if you show people whether products are in stock locally, they won't buy those products on your website.
B. [by implication] This is bad, because it "lowers" your sales. So you can't display this information.
C. [by implication] The retailers are making a mistake - the reason people don't buy products on the website when availability information is displayed is that they go to the store and buy the product there.
D. [summing up] If you measure something you don't care about, you will end up doing things that make you look like an idiot.
This isn't just hypothetical: for a while I was using QFC (Kroger) for grocery pickup, but after one too many instances of adding an item to my cart and then only finding out at checkout that a third of my items weren't actually available, I said to hell with it and switched to doing all that at Whole Foods instead, since their inventory counts are actually correct.
Try searching on Walmart to find local stock. You have to click "In-Store", then change the Fulfillment Speed to today and tomorrow to find things that are in stock. Except now they also show results from other stores, like Advance Auto Parts, and there's no way to filter that garbage out.
I tried searching Academy Sports for local stock. The list of items says it's in stock but when you go to the individual item it says it's OOS.
Lowe's and Home Depot local stock does seem to work reasonably well, for now.