I'm guilty of this, very few times will I buy DLC for SP games long after I'm done with them. My reason? I'll list them here:
- Not worth the effort getting reacquainted with the controls for a short DLC
- I've already beaten the main campaign and want to move on to something else
- There's a backlog waiting and I don't feel like delving into a game I've already finished
- A few years ago I'd have definitely been there for DLC of SP games the very day said DLC dropped, since I had time to play them and replay other games, now I hardly do and would just rather finish the game and move on to the next one.
For example, I'm currently switching between BotW and Nioh, both are going to take a long fucking time to finish, maybe I'll be over with both by the end of November (hopefully), both are the base versions of the game, no DLC included and I don't think I'll even bother with their DLC because there's Let's Go coming out soon, then Smash, then plenty of games already released on Switch that I want to try out, then there's RDR2, the Yakuza games I want to start playing, plus Sekiro and DMC V coming out next year, plus MegaMan 11 which I've had for like 2 or 3 weeks now and haven't even started... yup, I just can't justify going through the DLC of an SP game I'm done with.
I think the only SP DLC I bought on day 1 and played on day 1 was Left Behind from TLoU.
Despite loving these games a lot, I haven't bothered with their DLC yet: Horizon, Arkham City, Arkham Knight, Mass Effect 3, Bloodborne (I bought The Old Hunters, I'll play it one day), Spider-Man, etc.