People who want to astroturf, from everything from products to politics (though honestly probably more for "products"). Reddit is well known for being one of the few places you can "trust" product reviews (that hasn't been fully true for a while now but it's still valuable). If a near-0 karma and/or new account says "I love X product" then they can sometimes be downvoted/called a shill but an account that's a couple years old and has decent karma? Looks like a real person.

That's at least the explanation I've heard many times.