Well of course if correctness is not a requirement then it's not being paid attention to. That doesn't in any way indicate that it was a good decision not to require it in the first place.
If it had been made as difficult as possible for enthusiasts learning a markup language to get what was essentially text document to actually display anything, it's probably not too much of an exaggeration to say the World Wide Web wouldn't have existed in its current form.
It's not as if many of the web's security holes are related to whether a page displays valid HTML markup or not.
I don't think the assumption is justified that enforcing well-formed HTML documents would have been a significant barrier. To me it actually seems easier to have a few simple and strictly enforced rules than having a more or less random assortment of exception to save a handful of key strokes.
Ultimately it's less about saving keystrokes and more about amateur enthusiasts having the opportunity to start with the browser rendering their unformatted document rather than an "Error at line 1" warning, and changes they introduce being considerably less likely to break the entire page
XHTML Strict only solved one set of leniencies in the web platform, which were also the least important kinds. Malformed HTML makes writing browsers complicated but doesn't generally seem to cause security issues or other visible, obvious, must-fix-now problems.
The real security due to leniency problems in the web platform revolve around the handling of data and how JavaScript works, which were not addressed by XHTML. In that sense it's not surprising it went nowhere.
