And a lot of the firms that use it also tend to be large and have very deep pockets. You pretty much have to cater to their every need, because they pay well.
It is much easier and less expensive to pay a developer to keep writing those workarounds than to recertify all of the internal applications to a modern version of IE. Furthermore there is a significant time cost to the testing and deployment of a new browser to all machines. These two times and costs are often several times if not an order of magnitude or more the developer cost.
You're applying logic to a software issue at BigCorp, that assumption is, sadly, wrong.
A lot of the time it's some kind of support contract though. Somebody at some point in time had a brain fart and signed a contract for a Website running in IE9 for the next 20 years and now they will have to support that, cost it what it might.
- Academia (think: old internal course-registration tools or professor-used CMSes)
- Education
...are not valuable customers? Because those sectors, and many others, are famous for using old versions of software. IE9? Hell, some giant HealthTech companies mandate IE 6 for their customers with no signs of changing. All of those are areas where there is lots of money to be made.
There valuable customers in software that aren't only young, tech-literate people clicking on ads in a modern browser. Get outside the bubble.
That completely depends on the market you're in. Many governments are still on old versions of browsers and such, and they're also the only type of customer for our products.
tell that to the people that use it