Deprecating it if your site had much traffic was like pulling teeth! I worked at a company that had IT professionals as its main demographic in 2011 and it was a constant struggle. Lots of corporations were locked into IE6 because they had developed internal applications that relied on ActiveX controls or other non-standard APIs. IE7 was still pretty terrible, and it took even longer to drop support.

CSS was pretty bad but at least well-documented; debugging JS was a whole other hell. There was no such thing as dev tooling, and you got a small alert in the status bar when the page had errors, which opened a pop up that gave you the line number and very little other information. Supposedly you could connect it to VisualStudio and get a full debugging experience, but I never had the luxury. Lots of guessing and checking. Firebug was a huge deal when it launched.