Initial Steam was a horrible horrible experience, it also didn't have a store, and it was mainly just something you had for Counter Strike. Now, CS was MASSIVE, it still is, but that was enough to get a whole lot of people experience Steam.
It didn't help the internet connection back then was, to put it mildly, shit for most people, so a constantly disconnecting program wasn't a shocking outcome in hindsight, remember, this is 2003-2004.
It also felt unnecessary, you bought the game off Steam, Steam didn't let you buy anything and then anything not-made-by-valve, so why couldn't you just play CS directly, why did you have to install an additional app on your limited hardware?
And then things have changed. It's my go-to shop, and their contributions to the Linux ecosystem is much welcome. There's self interest, since operating a shop on Windows comes with inherent risks, but I don't see the same interest in other parties, so I'll take it over anything else today.