I work in the defense industry, which inherits some of the problems of its customer, the Government (in particular, a reluctance to spend money on infrastructure, reliance on policy compliance rather than personal accountability, and older, less tech-savvy decision makers). One of the computers on my desk still runs Windows XP, ironically because the security approval to replace it with a windows 7 computer didn't come through until just recently. So it is no surprise we aren't using wikis or IMs or Slack; I don't even know what the last one is (I mean, I can google, but I don't 'get' it; I've never had access to anything like that).
Few modern technologies can survive in this environment. By the time a 'new' technology is vetted by security, approved by the customer, and authorized by finance, everyone will have moved on to something else. But email remains. It works everywhere. It doesn't require 'special' software that the person you are communicating with may not have the IT permissions to install even if they knew how. Even the most out of touch customer representative knows what it is; you don't have to make slides about why you need this thing on your program. It can work over public networks and private networks; you don't need to trust a cloud or a young company. There are well-developed practices for using it. Lawyers and compliance staff thoroughly understand the legal issues (this is no small concern in a large company).