Just because the source code is available it does not mean it is free to use and do with it what you want. The license explicitly states that you may use it but have to publish it for free and follow the Steam subscriber agreement. Also this is just source code, not the assets (at least as far as I understand it).
You can downvote all you want, but that is the logical escape the industry will take. They will make the online part of games expensive to pay until no one wants to play it or pays them an absurd amount.
It can’t be that easy. PEGI says that games containing gambling (real money or not) are rated with PEGI 12 to 18. So there must be something else to the game that led to this rating.
But that of course does not include the games not running from Steam and pre-Steam games. So World of Warcraft is somewhere in there too. And the final Top 1 must be Transport Tycoon Deluxe (even if you don’t include OpenTTD).
Titanfall 2: You have a titan as a companion for most of the game (there are segments where you’re on your own though). And it’s a fantastic single player campaign.
I started playing it last year because my nephew wanted someone to play (apart from his friends at school). I kept playing it on a regular basis (I had bought the base game years ago, but have not paid anything since). I enjoy the colorful graphics which run fine even on my 10+ old gaming PC. Some rounds are short and you’re dead within minutes but often I reach top ten, but even then the rounds aren’t taking that long (20 to 30 minutes), which is something I like about the game, because I barely take the time to have hour-long gaming sessions any more. Despite its looks skill makes a difference when it comes to aiming and movement (most special weapons are movement skills). I mostly play the no building mode because I can’t manage shooting and building at the same time.
Of course there is always OpenTTD, which has by far exceeded the original, but I would just like to see a modern game (not necessarily in terms of graphics) with the same vibe. Transport Fever and all the other variants never quite achieved the same depth and complexity.