For me it's the same as Klumpen and doragasu say.
They use user data to help select games for Steam sales, they notify you when one of your wishlist is on sale, they recommend things based on play history.
Oh no, they send me an E-mail when a Game on my wishlist is on sale.
Isn't that exactly why you put games on a wishlist?
Should I be angry if bandcamp (online music store) sends me an E-mail if there's a new song/album of an artist I do follow?
If so, why don't I stop following artists but make a private list of Artists I want to check from time to time.
Selecting popular/unpopular stuff for sales?
Oh come one.
If a store wouldn't watch what sort of games it's customers like then they can stop selling stuff right away.
Let's go further:
DragonBox shop does the same in some sort.
We see that lots of people buy some specific products so we want to have them in stock.
We also see some products do sell badly, so we might not want to get more of it or maybe do a sale to at least sell them for buying costs.
There's even a wishlist. If you sign up you'll get an E-mail if a product that's not in stock rigt now is available (oh no, how evil, you get informed if something you want is availabe).
If you don't watch your customers then you don't need a business.
Difference is we don't collect personal (!) data or sell it to someone.
We don't collect data from customer Messages or other personal/private.
In some way you have to watch what sells good and does not. Then you can make special offers and such.
Of course you want to sell stuff to people if you have a business but you can do it in an evil or in an ethical way.
Sending E-mails to customers who signed up in a wishlist because they want that E-mail and giving special offers for products a lot of people like is no misuse of personal Data.