> I think they've just become a de facto thing that is expected.
Good god! Where in the world are you?
Here in Blightty, it wasn't that long ago having a linkedin account would count against some of our candidates.... as a candidate must have had their head in the sand not to be aware of the toxic behaviour of linkedin (spamming personal contacts) [1].
[1] https://www.theguardian.com/technology/2015/oct/07/linkedin-...