The sweet spot was getting the full game on disc and getting included DLC, having the ability to mod the game, and run private servers.

You could just enjoy the game as-is with a really good singleplayer campaign and then with whatever online offered.

Some of the mods from this era turned out to be just as popular, if not moreso, than the original base game. Some of them live on to this day.

Sure, some Steam games offer mods and the like, but it certainly isn’t the same thing as what we had 15 or so years ago.