Many peoples prior experiences with manufacturers have taught them that manufacturers frequently aren’t helpful when it comes to solving problems: assisted support takes too long, makes you wait, is staffed by someone halfway around the world who doesn’t speak your language well, makes you redo the steps you already did, and doesn’t have the expertise to solve the problem. 
And unassisted support is poorly written, as though by someone who isn’t even human, solves only general problems for general solutions but not the specific problems that real-world people encounter, and just isn’t helpful.
In response to this, customers frequently turn first to Google to find help for their problems. Google is fast and easy to find the top hits relevant to their problems. They don’t care where the help comes from – in fact they trust help from a stranger on the internet more than they trust help from the manufacturer. 
The stranger has no inherent agenda, while the manufacturer has many agendas that run counter to the interest of the customer: to keep support costs low, to sell the customer more products, to keep embarrassing problems from leaking out. 
The stranger proves his worth simply by sharing information when there is no gain back to him by doing so.