People do self vote in the ways you're describing. Leo voter will upvote leo content, for example. Splinterlands will upvote Splinterlands content. Holozing will upvote Holozing. And so on.
This puts product placement ads all over the place and the creators act like sellouts to get those votes. It's a real downer in some ways especially for the artists since when they deliver their own style, they'll make a lot less on average.
Just another issue that's quickly resolved by attracting people actually interested in supporting content, the real way (strange I have to add that "real" part in).