Why? Because it's so bloody frustrating. I don't expect to change your mind and I'm not trying to shame you, I just cannot understand how something that is so well document and has been proven time and again is still subject to 'debate'.
Everyone is entitled to their own opinion on unsettled matters and on how they feel about things. But some things are just true - they are scientific facts, they are proven, and those things are not up for debate. Moon landings, human influence on climate change, vaccine efficacy - no, your opinion on these is not just as valid as anyone else's because they are scientific facts.
There are countless links on this thread to debunkings of the conspiracy theory but you still aren't convinced, which leads me to believe there is in fact nothing that would convince you, short of landing you yourself on the moon.
And not only is this frustrating but it's actually dangerous. Is anyone damaged by you not believing in the moon landings? Not really... but conspiratorial thinking of that kind is the same as believing Andrew Wakefield had a point about the MMR vaccine, and it's thanks to people taken in by that that we have children dying of measles again.
So pardon me if I'm a bit fed up of this bullshit, but that's why.
That is of course assuming you really believe this and are not just winding us all up. Which frankly I would prefer.