Actually many do.
What are you basing your opinion of this on? I'm basing mine on first hand experience FYI.
My prior group (that I still help out from time to time) was the very definition of midcore, capable players, laid back schedule, no big rush to clear the progression content. Most of the group worked together with a few extras and got pretty close to Golden Bahamut from memory and once again, they've recently gotten going properly in UWU as well.
I'd also consider my current group rather midcore even if we do clear within the first couple of weeks, mostly down our extremely lazy running hours and almost complete lack of interest in speed runs. Again, 3/8 of the group's seen up to Titan with various pugs and PFs, the rest entered for the first time with us as a full team yesterday. We're working on it (tm)
Then yeah, we are working on a different definition of the term.
My group most certainly isn't hardcore.
Personally I think they don't have the manpower within the team to keep creating it, but that's a discussion for a different thread.