That may just be the first time around when you get to the tenth room; another reason would be that one of the upgrades, "Heavy Drop" says something along the lines of ensuring that every pinata will get a chance to drop at least 2 toys.
Here's a screenshot of my first time clearing out room 10, did the same thing, but never again afterwards
Although whose to say? I'm not even the developer of the game I am just a consumer ¯\\(ツ)/¯
