Because most people think that the Hunter Exam in the manga sucks. Even manga fans say that. It's bare bones and the characters hadn't had sufficient time to develop, or rather they were sparsely developed. The first two phases were simple and boring. It only got interesting at the third. The fourth was anti-climatic and Gon's fight didn't convey itself well in manga form.
Whereas, because of the proficiency of direction and the added content (or filler), the Hunter Exam in the 1999 anime was awesome. Sure, there were some stinkers like Illumi v Gon but that was really owing to inconsistency of character/plot, rather than poor direction or poor scriptwriting. Anita wasn't too good either but it was tolerable. Everything else worked incredibly well.
If people think the Hunter Exam was "boring" then they are probably not the target audience of Hunter x Hunter.
First exam wasn't boring. Sure it wasn't really action-packed. But it had good psychology behind it.
Even from before the exam starts Tonpa is crushing rookies and Hisoka is cutting their arms off.
Then you got the exam itself---an insanely long foot race with no end in sight.
The characters were "sparsely developed" but then they should be. Character development should
be gradual. Not all smacked in at once.
And then let's not forget the next half of the first exam Swindler Swamp.
That was boring? Seriously? You're telling me a swamp that's trying to eat
you and get deceive you in so many ways...while a murderous magician
butchers examinees and you're left wondering will Gon even SURVIVE the exam?
Second Exam was comedy relief mainly.
3rd Exam Trick Tower was a chance to go into further development into each character.
Gon is shown to think outside the box and isn't just the standard stupid shonen hero we thought he would be
Kurapika's rage for revenge is shown and he's not as calm as we once thought.
Tonpa's motivation is explained
Leorio isn't as dumb as he looks but he plays it too safe
Killua is dangerous and the others are a tad bit worried about that...except for Gon.
4th Exam Zevil Island. Pure awesome.
Final Exam. Anticlimatic. Yes. But then that's the point. You're supposed to be like aw shucks that was it.
And then get this....THE EXAM WASN'T REALLY OVER. How about that? We're only getting started.
Exam ends with Hatsu training and now Gon is ready to fight Hisoka...Which ends up being brilliant.
But if the Hunter Exam is boring then I don't see how the 99 stretching it out and adding filler made it more exciting.
The tunnel with the sap or whatever was stupid and cliche. Oh no it's a sap that give you nightmares! Let's use
it as a way to shoehorn in some melodramatic flashbacks. Anita filler was annoying. Battleship exam wasn't so great
either. Hisoka vs Kurapika was alright the first time seeing it. But then after a while I realized how stupid and cliche it was.
Kurapika "I will win with my pride!" (Ok he never said that. But he might as well.)
I use to think the Hunter Exam was boring. It's true. Do you know why?
Because I saw the 1999 series Hunter Exam FIRST.
It wasn't until I read the manga that I was like...wait...THIS IS AWESOME.