For years now, I've seen many restaurants rely on an Instagram account instead of an actual website. It's definitely easier for them to create an IG account than to pay someone (or a service) for a website. Also, posting to IG lets them market to their audience (instead of posting it to a website that presumably fewer people visit).
Shame since I often want to view their menu, and IG is really aggressive about not showing you profiles & images unless you login. Viewing their menu on a 3rd party site (Google Maps, Yelp, delivery services, etc) is subpar and often out of date.