We always, always hear the same threadbare stories about mythical magical enterprise customers that can't/won't upgrade, and the little tail wags the dog, and the life for the rest of us is made harder.
All this for a use case which is basically hearsay and rumors.
As for inexperienced developers--I'll go and say that the experience I've had of watching bad compilers and system headers and christ only knows what else force native code to get uglier and uglier and less maintainable are what motivate me to try and discourage the same mistakes in Happy Web Land.
The web is barely twenty years old, arguably much younger--let's at least try and avoid sins we don't have to commit.
Edit: Or, you know, downvote me without explanation. That's pretty cool too.
Note that I'm not a decision maker - in fact, I'm not even in the IT department. Please don't try to argue this with me, as I may be totally wrong about what their decision factors even were. Personally, my life would be much easier if they would upgrade, but I can understand why they have not.
But I will give you a clue. Go find a list of the top 10 biggest banks in the United States. It's almost all of them. Then go find the biggest credit card companies. It's most of them.
Find me a bank that doesn't run IE, for that matter. I'm a Chase customer, so I can only confirm them. But I honestly wonder how many banks don't run IE.
I know of at least 2 big blue chip companies with this problem.
In fact, I once had a requirement that the software we write have it's own independant auth mechanism and NOT be linked to Active Directory, "because it costs us thousands every time we ask to add a user or change a role".