Okay, there are three possible outcomes.
1) I switch in Absol on something that's set-up fodder
I use SD as they switch to Conkeldurr (assuming I even have SD). Conkeldurr sees that I'm at +2 and can't risk it and uses Mach Punch, b/c +2 Psycho Cut OHKO's.
2) The opponent switches Conkeldurr in on something that's set-up fodder
They Bulk Up as I switch out to Absol. The opponent wonders why I switched to Absol, assumes it's some revenge killer, and uses Mach Punch for an OHKO. If they don't use Mach Punch adn continue to set up, you can snag a Bulk Up, but now you're both at +1. The next turn, Roobushin uses its boosted Mach Punch and OHKO's.
3) There is a rare double switch in which you bring in Absol and the opponent brings in Conkeldurr at the same time.
The opponent assumes you will switch out, because this is normally a bad match up for you, and decides to Bulk Up. You steal it and get +1 in Atk and Def. The opponent tries to kill you with Mach Punch, but it doesn't OHKO and instead I deal 89.2% - 105.5% to him with my +1 Psycho Cut. Assuming it doesn't OHKO, I can kill him next turn with Sucker Punch before he can Mach Punch me.
Out of those three scenarios, only the third (and rarest one) succeeds. You're not going to be killing Conkeldurr any time soon, and SD Absol is pretty much better all of the time. SD Sucker Punch is great on Absol and is better than any Dragon Dance, Bulk Up, or anything else I can snatch. Sure, I am more open to revenge killing with SD Sucker Punch, but Snatch is unreliable and still can't beat Conkeldurr.