I have been playing computer games since the late 90s and for me steam hits all the important things with few of the downsides that existed prior to an online storefront.

Games had DRM prior to steam and other online services. A key you had to keep track of, something from the instructions, or in some cases an online authentication process. All of these could be lost or the online component be retired and you ended up needing to hack the games anyway.

Games often had issues over time due to a lack of ongoing support. Driver issues or other problems might cause a game that previously worked to fail after a decade. The earliest game I remember with that issue was Crescent Hawks Revenge which was tied to the processor speed and over time it sped up so fast that it was unplayable as games got faster. Again, it was necessary to hack the game or the PC to address the issue. If the games did have updates, they were often tedious to find and install.

Games on PC have pretty much always been a license to use and not actual ownership. If you read the EULA you were banned from hacking to fix the issues I already mentioned just to get it to play.

Then there is a personal thing I noticed which was that I didn't want to put forth any effort for older games just to play them. Like, sure I might want to give it a spin for an hour, but not if it took an hour to address issues due to changes in hardware or software since I last played it.

So along comes steam and while it had a rough start, it solved all of my computer gaming issues. Games were perpetually maintained, so if I bought an older game it would most likely work on current hardware. Sales meant I could afford to try out new games at a decent price! Games updated automatically when one was available and I didn't need to do anything extra! Every game I have purchased from steam can be downloaded on a whim and be expected to play. Maybe there are some exceptions, but I haven't run into any.

Only one game I purchased stopped working because it was multiplayer only and the servers shut down. Owning it outright wouldn't have mattered.

While it is possible that steam could shit the bed at any point in time and I could lose all the games on it, the value for the money has been totally worth it. I am glad that there are alternates and that GOG exists for DRM free versions of games, but the ease of use and reliability that I have had with steam has made it worth far more than I have paid into it.