I was always told that the reason you used to see an Olive Garden next to every Red Lobster is because a husband/wife couple owned both chains and wanted the restaurants placed next to each other. Then a decade ago when they kinda stopped doing that it was because they divorced.
I can’t find a single piece of evidence that supports this claim online. The two restaurants were just owned by the same parent company and Red Lobster got sold off in 2014.
This is it. Modern planners use GIS and data analytics to place new stores. In my region Publix and Starbucks are a common thing and usually going for similar demographics, so it's not unusual to often see them in the same shopping plaza. Similarly dollar stores, Walmarts, and Dunkin' Donuts always seem to find a place in the same neighborhoods too (in my experience). Those Dollar & Dunkin' neighborhoods almost never have a decent grocery either.
I've heard that Starbucks spends so much doing neighborhood research and real estate trends that if you buy property anywhere near where they are building a new Starbucks, you are likely to see a positive return.
Something like that happened in my town. A husband and wife owned two Chinese buffets across town from one another both called Hong Kong. They divorced and each kept one, but the husband renamed his Blue Fin. Blue Fin shut down about a year later but that other Hong Kong is going strong.
We had that in my town with Walgreens and Osco Drug. You'd literally see them across the street from each other, and you'd rarely see a Walgreens without its Osco... Then suddenly all the Oscos went out of business and were gone forever. It's kinda amusing whenever I visit the old home town, because there are multiple buildings that still look like no one has taken the buildings over after almost two decades cuz you can still see the outline of the old Osco signs.