This was just penance for the "green" flavored Hostess cream pies they were shilling. Remember kids: next time you're at your grandma's house, take a couple of Light & Lively Yogurt packs with you. She doesn't even remember that she bought them!
The turtles discover yogurt, yet never question why Leonardo is shilling the stuff on a billboard directly behind them. Perhaps they're distracted by the fact that they all have the same voice.
There was once a time when it was possible to go a full day, from waking up, to going to school, to coming home, to going to bed again, without touching something with a TMNT logo on it. I am living proof.