I don't trust the platforms you cited, so when I want to call a restaurant and they want my business, they must have a website.
Besides, I don't want a third party asserting itself into my relationship with the restaurant.
If I am considering patronizing an unfamiliar restaurant, and my only source of information about it is some untrustworthy third party platform, I'm moving on. Like I said, many restaurants exist, I'm losing nothing by going somewhere trustworthy.
And again, I cannot emphasize this enough: I do not want some third party asserting itself into my relationship with the restaurant.
Neutral carriers and infrastructure providers have shown decades of tolerable neutrality [0], and are obviously a much different (and lower) threat model for contacting restaurants than the "Instagram/Facebook/{delivery app}" third party platforms to which I referred. These platforms have proven, year after year, to perform despicable acts of surveillance and experiments in psychological manipulation. They're called out for it, and they sometimes apologize and promise to "do better" in the future. Then they immediately go back to performing their creepy shit without remorse, and the cycle repeats.
"Fool me once..."
[0] Carriers and infrastructure providers certainly have unacceptable problems selling data+metadata to third party platforms, and I also note with righteous fury their enabling of illegal, unethical, and creepy-as-fuck government wiretapping and eavesdropping. They do not, for example, intercept my orders by showing some phone number other than the restaurant's. They don't disguise their call center as a restaurant's phone line. Their creepy psychological profile on me is less granular.
Someone might claim, "Oh, but Facebook has never done anything like that." Neither did Yelp or GrubHub or the others, until they did. These platforms have shown, over and over, they cannot be trusted. I'm not going to trust these middlemen. I can have a relationship directly with my food providers, and it benefits the provider and me, without worry that some asshole will someday decide they will manipulate me or the restaurant, simply because they possess that dubious ability.