That may explain why many won't shop elsewhere, but it's also part of PC gaming platform's long-term problem. Prior to 2004, it simply didn't matter where you bought a game from as the discs were the same from Gamestop as they were Electronic Boutique, Amazon, mail order companies the local family run indie store, or even 2nd hand on Ebay / a flea market. No games were artificially crippled to deliberately *not* work when sold by other stores beyond the "first" / largest one. Developers patched their own games directly from their own website (only one patch needed for all stores). In-game achievements (eg, Dragon Age Origins) worked identically on every platform (even DVD-ROM on a 100% offline machine).Thing is, when you have spent so much money on one system, say steam, and have a lot of games on it, there is pretty much no way any other is going to be anything but secondary. Also if you could get the game on your primary system, steam, chances are, you would. I have hundreds of games on steam, so i primarily only look on there for games.
Then in 2004, along came Steam. "Online distribution" of games themselves (instead of patches) may have been "revolutionary" but the decision to start locking 3rd party (non Valve) games (then later on features that really should have been in-game) to the store that sold them was and still is massively anti-consumer regardless of how "convenient" some deem it. The equivalent of Walmart "being first" to sell DVD's but instead of just selling neutral discs & Sony / LG, etc, players, they instead specially made their own deliberately incompatible Walmart DVD player that required discs to be specially mastered just for it would have set up an artifically high barrier to entry for every following store, massively increased workload for studios having to remaster new versions per store, and made the market a huge mess for real competition. That's post 2004 PC gaming in a nutshell where even very pro-consumer stores like GOG are still suffering from store-front tribalism (aka "No Steam, No Buy" cult like attitudes) that were 100% started by Valve back in 2004.
People bitch & moan about needing more than 1 client and yet Epic's exclusives have actually reminded people that forcing the use of any client (and underlying DRM enforcement) negatively affects everyone and has done so all along since 2004. "Captive audiences" are only re-noticing it more now because a game is not on "their" store. Now we're also seeing some of that turn the modding community gradually toxic where formerly platform neutral free mods on Nexus, etc, are being "gated" being Steam Client paywalls, which very definitely isn't what the open modding community is or ever was about, but the same people up in arms over Epic's exclusives will shrug at Steam Workshop exclusive mods because it's "my store", not "their store", little different to the tribal bullsh*t we see on consoles. So whilst I don't like Epic's exclusives myself, my response to anyone pushing "Epic exclusives are so anti-consumer" simultaneously with "No Steam, No Buy. Steam Workshop exclusive mods are great" is "Cry me a river..."