You really should never ask someone to speak on behalf of everyone else. Fortunately for you, I am one of the very few who is eminently qualified to do so, and will indulge your question.
There are a few reasons. Firstly he’s a kiwi, and their efforts are sometimes not as well recognised as others.
Secondly, he had the disadvantage of being around in arguably the best era ever for fast bowling, so he didn’t stand out as much as if he’d been the dominant and stand out bowler in another era, like Steyn as an example.
He may also not get the kudos given his home decks were considered NZ green tops. I think that’s unfair but it’s a perception.
There’s an element of him being so far ahead of his team mates that he would naturally take all the wickets. Again, I don’t know that I agree with that, there’s benefits being a clear number one in a side, and there are others being one of four guns like the WI blokes of the same era.
I also think Hadlee’s batting is being massively over rated here. He was no more than a very average number seven or very good eight at test level, and I say that as someone who saw him bat a lot. He had a great eye, but of the four 80s all rounders, he was by far the weakest with the bat. He was sort of slightly worse than Ian Healy level with the cue imo - no mug at all and scored valuable runs, but nowhere near the batsman the likes of Botham, Khan and Dev were.