Let's be frank, that kind of people are the ones who don't even give a damn about others.
Sure this is a pirate forum, but most are actually goodwill pirates who still try to support the dev, since any kind of support is important to at least keep the project alive.
What differs these forums from other piracy forums is that there's a of community out here, as well a sense of encouragement for the devs to actually talk with their fans out here. Finally, the forums provide tools for the dev's patronage and socials instead of straight stealing. The provision of mirrors does also avoid the dev's original links to be flooded with movement, protecting it's property at least.
Finally, those who leak untested versions aren't providing a favour to both dev and fans. Sure I also want to play, but I would much rather wait and have a stable version than a rushed one. A stable version gives good feedback and encourages the dev to continue his project. Not to mention the possible increase of patronage, some games around here I ended buying or supporting the dev, and I'm sure others did as well.