Payday 3 is 'always online' and will require an internet connection, even if you're playing alone with AI, say its developers.
Another "always online" game that forces people to connect to internet while playing single player.
Even though most people do have internet access these days, it is still not a good development when you consider some places have less stable internet than others. And also what happens to the game when the server shuts down.
...you can play it with bots? That's kind of how any 4 player co-op game works lol. I don't remember Left 4 Dead 2 being online only when I wanted to play by myself. Payday 2 already has a whole community of people who play the game by themselves. In fact I believe you can even disable the bots and do the whole maps solo.
Usually because they want to sell you cosmetics and other junk and the only way to ensure you don't just mod it in for free is to make the game phone home and verify itself constantly.