Because I feel single day riders and sprinters are discredited this way. You already have the same amount of chances of winning a stage during a stage race for mountains and TT, as a sprinter for a flat stage, and now you also get an extra point if you win the whole thing.
I don't think fairness really matters here.
In the end the sport is about winning one-day races and winning GC's.
By winning a GC you won a contest as the sport defines it and unlike a sport like football said contest is not made up out of the sum of other contests (e.g. winning matches = winning competition) but is a separate category entirely.
It's not something that gets added on top of things to just ensure that 'the rich get richer'.
Cycling is odd in this regard because almost the same distinction can be made between TT and RR. Very different disciplines yet both count as a win.
However, I generally do not accept subclassifications as wins which I know some people to do. Reasons being that these can be basically made up, it is hard to make the distinction between what should and should not be counted unless you want to count literally every rule-based subclassification and it is not what the sport is about.
After all any race organiser can come up with some dumb Hammer Series like system to base a subclassification on.
Perhaps it could be argued that SOME subclassifications such as points classifications are accepted enough to be counted as wins too. I have no doubt that someone can point to the distant past where points classifications were perhaps orginially used instead of time in some races. I think this one has the most merit out of all subclassifications.
I am also torn on TTTs but do think they should be counted.