while i would give these businesses the benefit of the doubt, i would also say that the responsibility is on them to know. Ignorance isn't a real defense imho.
It's true that making an independent site to host your updates and info isn't as easy as just posting to facebook/twitter. I understand why a lot of businesses, esp. small ones, don't bother. Each rain drop also don't hold themselves responsible for the flood.
IF they made the decision. There is more and more people there who doesn't even understand the concept of a website.
To them 'being on the Internet' equals being on Facebook/Instagram.
It is hard to make a decision about something you don't even know.