Just my two cents as well.
Microsoft's internet browser breaks a lot of rules both in backwards compatibility and also some WWW rules. That being said, this can be said for many of the browsers.
However one thing that is clear is Microsoft's share of users actually using the browser (particularly from technical users as opposed to general users) is that it is vastly diminished.
Have a look at the following site.....
http://www.w3schools.com/browsers/browsers_stats.asp
Microsoft lost a lot of users in the last 4-5 years as many started to realise the value of other browsers, and also how "integrated" or "Woven" the Internet Explorer is in their Windows OS, which in general meant, get a problem with the Browser, and have an issue with the File explorer etc (and vice versa) and in some cases had to use Firefox or Chrome to get round the issue.
If you look at the coding required to support backwards compatibility for the Internet Explorer (and still not get things right), it becomes an easy measure to ignore Internet explorer or limit your support for various versions.
I was on a job today, and configuring a router with a GUI.....took me a while to realise that the problem I was having was with Internet Explorer and this router GUI (it was corrupting the settings saved)....I only used IE as it was quickly available. Loaded Chrome - finished changes in a couple of minutes - no issues.
Now what I have said can be debated back and forward......
However one definite reason for the support of Chrome and Firefox is that they are cross-platform browsers, supported on Windows, Macs, Linux, Android etc....
Then you add in that you cannot run the Internet Explorer 11 on older machines (where as you can with other browsers). The reasons are understood, as some of the functionality that IE needs to tied into the OS system, but again you have developers that need to handle this and With the amount of work (additional coding) and testing to check whether IE works, it is just not worth it for many Software developers to look after a browser that is tied to one OS and with a diminishing client base.
Sorry more like 20 cents worth.....but you get the picture
Regards
Bob