Spot dodging takes 22 frames, definitely enough time for a punish. Pikmin toss has negligble lag after the pikmin is thrown.It's the same reason any other random projectile camping can't work: Perfect powershielding. Replace "powershielding" with spotdodging or your fastest attack, since PSing doesn't stop Pikmin latching. Unfortunately, we lack frame data for Olimar's attacks, but I can only assume the Pikmin Toss is too laggy for Olimar to punish a well-placed spot dodge or fast attack used to knock away the Pikmin. Even if he could, Olimar isn't fast enough to corner most opponents into the circumstance and long-range opponents (Marth, etc.) may well be able to punish the Pikmin Toss itself.
Why need for corner? You start out the match too far for melee but the perfect length for camping. And after all, you have to come to us, not the other way around.
If Marth is close enough to punish, we either walk away, or we grab.
Pikmin toss has a pretty high rate of fire.