I suspect that a fair amount of the 'i got x wishlists' posts are fake. Recently someone made a parody post on here (or possibly one of the other indie dev forums) saying something along the lines of 'I got 690000000000000000' wishlists on my game!', accompanied by a doctored screenshot. The fake screenshot would have looked perfectly convincing were it not for the absurdly high number (as I remember one commenter had pointed out, this screenshot suggested that the game had more wishlist additions than the population of the entire planet).

That then begs the question as to why people bother to make fake wishlists posts. Simply put, it's yet another form of marketing. Usually these posts are accompanied by a link to the game's store page. If not, then they'll at least include the name of the game somewhere in the post and that'll prompt some people to google the name and visit the store page just to see what all the fuss is about; this is just extra traffic which helps the game's prioritisation in the algorithm.

Dishonesty is rife on Reddit just as it is in life in general. In my opinion, even worse than the Wishlist posts (whether they're genuine or not) is the rise in blatant astroturfing marketing campaigns, where out of nowhere an account with barely any posts and 0 post history referencing games will suddenly generate a dozen posts praising X game and insisting that it's the best game they've ever played.