What usually happens when you come in on Chansey or something is that you get a wildcard like Altaria that you know you can't beat and you get forced out anyway. Spikes and SR are probably on the field, so you're going to take way too much damage if you try to switch in on a resisted attack. Best choice of action from here is to try and come in on the revenge and they repeat the process. A stall team can usually dick around like this with an offensive team, wearing you down with residual damage by abusing the fact that no one sweeper can cover everything.
That's why non-offensive moves like Encore and Taunt work wonders for breaking stall by allowing you to screw over and set up on even the sturdiest of walls. A team with a simple lead, a few sweepers, and a couple of walls won't do shit to stall; you really have to broaden your horizons if you want to cover as many playstyles as possible. Magmortar and Blaziken are useful weapons against stall, but you're going to need more than that to get the job done. Encore Poliwrath and Taunt SD Drapion are huge bastards for stall teams to face as well.
