Gabe Newell talked about this years ago.

“When you look at the fact that these people have $2000 PCs and they’re spending $50 a month or more on their Internet connections, clearly they’re willing to spend money.

So, from our point of view, what we saw more and more was that piracy is a result of bad service on the part of game companies...”

malware? bro you can redeem the games on their website and use an alternate launcher to install them.

Steam just works better. Their cloud save is reliable, and library organizing is actually a thing. I can see someone using the free Epic game as a sort of demo. Plus, if they really liked they game they may want to support the developer

The article suggests that people are willing to pay to have all their games in one place.

A not-insignificant amount of people would rather buy a game they just got free than have to remember to open epic.

Because its easier on Steam, at least for some (on Linux, or no hassle on Steam Deck in example) with more features if you care that too. Often the games are on sale on Steam too, so its not like paying full price. I think what is actually happening is, that people read about the game, find it interesting, the articles talk about it, people ask or want to try, because their friends tried maybe. And then they buy it on Steam, because they do not care giving a little money (me included), and don't want to mess around or use Epic.

Back then when when the GTX 970 was brand new, I got Witcher 3 on GOG for free buying the card. A little later I purchased it on Steam, because I wanted to have it on Steam. And because the updates were somehow broken on the old GOG launcher... But that's another story. The point is, lot of people prefer Steam over the other stores / launchers for multitudes of reasons and buying the game is not a big deal for most. Depending on the price off course.

I would assume the people buying it on Steam while it's free on Epic aren't bothering to claim it on Epic, so they don't "already have it"

You can, but it requires some setup in the desktop mode. I guess some people do not bother or don't know you can do that.

People hate Epic* games.

Probaly coz people start talking about the game again after it was free and others jist buy the game on steam after reading the social chatter

I don't think that's what's happening. It being free on Epic made people discuss it, then people saw that and purchased it on Steam. That's my assumption at least. I'm sure there's some people who just wanted it on the Steam launcher, but I'd bet on that being a minority.

It's been great advertising for sequels. I got 20XX free on Epic, then bought 30XX on Steam when it came out. Great games.

The whole idea isn't the advertisement on itself. The idea for the publisher / developer is, to take the money from Epic, as it seems to be a lot. And for Epic this is obviously a reason to get users into the eco-system. That is the basic idea behind it. That games get free advertisement alongside, is a nice bonus effect.

Epic game store freebies are the demo..

Which one? I love TD games