I don't know, if you find someone who has been posting for 3 1/2 years and questioned every post and news announcement, you'll have to ask them.
As far as "vested interest", are you asking why anyone would post about a stock if it wasn't going to provide them with a financial reward? Because they enjoy contributing and helping others make better decisions? That would be my first choice. Do YOU really think that the only people who post on stock MBs are those who can personally profit financially from their posts? Thankfully, I think you can see that's not the case, otherwise the MBs would not be of any value. IMHO.
'Tis better to be silent and be thought a fool, than to speak and remove all doubt. - Abraham Lincoln