What I can't understand is why a DM didn't stop the divers from touching the shark, since that's a big violation of marine park rules.
The first person it approached was a DM. He pushed it away, but didn't pursue contact with it. However, other divers saw this contact and may have taken it as license to mug the shark. The group was fairly spread out, so I'm not sure how the DM's could have stopped this once it started.
1. While this is odd behavior, we really have no evidence that anyone has fed that shark.
Apart from behavior demonstrated in the video?
I have watched the first DM feed sharks from his ELF on other dives (the one who took the video will not feed fish). Given how similar one nurse shark looks to another, I can't prove through having witnessed feeding that people have fed that specific shark, but I believe it's a very reasonable inference that satisfactorily explains the behavior.
If you don't think feeding is reasonable to infer, please offer a reasonable alternative explanation for the behavior. Make sure it covers extra attention paid to DM's (who are typically the only divers likely to be wearing hooded vests and shorts and to be carrying ELF's within the Marine Park) and to the shark's particular interest in the divers' hands.
2. as someone said above, WTF were they doing reaching out to pet it?
Molesting it for their personal enjoyment.
3. if this in the marine park, WTF are divers doing wearing gloves?
It was in the Marine Park. The gloved divers were Japanese and, according to my wife, either had significant issues understanding that they weren't supposed to have gloves or were simply stubborn. My son thinks they donned the gloves underwater, but my wife isn't sure. A DM took their gloves away during the SI and the entire boat was sternly lectured not to touch anything and told anyone pursuing animals to touch them would be banned.
By then, of course, it was too late.