For me it was Terraria, Satisfactory, Tetris Effect Master Mode, Minecraft with Mekanism mod & CSGO / CS2 (almost 2000 hours in CS alone).
Edit: There are so many answers that I might only reply if I have something interesting to say. I will read all of your answers though. 🙂
Edit 2: It has become too much for me and I have to disable notifications. Thank you for the massive response and please continue to discuss with everyone here. ❤️ 🫡
Consistent habits.
The couple of games where I got those types of playtimes were either things I had semi-perpetually running for long periods of time (because reasons) and one game that became my “one hour decompression post-work” for maybe three or four years. Turns out if you do a thing consistently for a couple thousand days in a row it adds up.