It's a case of first impressions for a lot of people especially if F is generally something not deemed affordable or if you haven't a company paying for it.
If I've spent say £3k on a F flight to JFK and set my bar at a level that most of us would consider to be a first class experience with a price tag to boot, then anything less will disappoint and leave me with a negative opinion. I'll probably not repeat as well.

There are those here who know what to expect so don't expect the red carpet treatment, 5* food and being waited upon hand and foot, or suchlike.
But for someone not in the know who reads the blurbs on the website about fine dining etc. and sees rich people living a luxurious first class lifestyle, it's not hard to find many faults in what is presented.
It's like going to a fancy Michelin starred restaurant and paying £200 for someone to walk around with a bucket of gruel and slop it onto your plate - reality doesn't live up to expectations.

Well, maybe not that bad but as I've said before, a bad first impression is hard to change and you notice more and more faults which detracts even more from your expectations.

Even my last CX F flight wasn't quite as good as previous flights. Few things changed and left me not as enthusiastic as other times and/or my excitement for it wasn't maintained.
As nice as it was, I may look at other options should I be taking similar routings.