Sadly, Microsoft deserve a fair amount of blame for this, for not ever really supporting XHTML in IE back when it was so dominant. Oh, I mean, they "supported" it in that it would render, but they didn't support the application/xhtml+xml content-type, which mean that, in turn, nobody served their XHTML as application/xhtml+xml, and so on.
I won't say the lack of widespread adoption of XHTML was all Microsoft's fault, but they definitely played a role.
I won't say the lack of widespread adoption of XHTML was all Microsoft's fault, but they definitely played a role.