Please understand that a web browser is just a software tool like any other. You don't install a web browser at your business so you can say you use some bleeding edge shiny. You install a web browser to get some useful job done. Much of the time, that involves accessing in-house systems. Some of the time, maybe it involves accessing the external WWW, perhaps to research or buy something. Supporting the latest browsers so everyone can spend even longer playing on-line games or posting on Facebook is, shall we say, not a business priority.
Now, please understand that perhaps the single most important attribute for most large businesses with significant IT operations and mostly non-technical staff is predictability. If everyone is running on a stable software foundation, then tools can be built on top of that foundation. If everyone is running the same version of their end user software, then help desk staff can provide canned step-by-step guides to doing things, or remotely access someone's machine to fix a problem or guide a user through a new process for the first time. If every server in a group is running the same operating system distribution then you only have to keep track of one set of security patches and apply them uniformly. And so it goes on.
In this context, it is entirely reasonable that businesses "refuse to run modern browsers". Your modern browsers do stupid things like moving the goalposts every six weeks (or every few months if you jump through special hoops to use a laughably named long-term support version). Your modern browsers include new technologies that introduce security and privacy risks we didn't have before. Your modern browsers break backwards compatibility and won't run the $5,000,000 bespoke CRM package on our intranet any more! And in most cases, your modern browsers offer no business benefit compared to the tried and tested tools already in use.
In short, while you may wish that everyone ran the latest shiny new browser, there are very good reasons why many big businesses don't. If you think the guys running IT for those places somehow didn't notice that there are other options or just can't be bothered to upgrade or suffer from "intellectual sloth" then you really have no idea how things work at that level at all.