There was a message along with the mushroom hut opening stating:
"Treat bags will be added shortly!" and they were added not even 30 minutes after the mushroom hut opened.
Also, there is no way to purchase candy with gralats. So I heavily doubt it's "greed-driven" since makes zero sense.
Keep feedback to submissions. (the forum topic)
Still seems weird not to release it all at the same time though, i mean, it was my fault nonetheless and i never saw the message, but still, why not wait another 30 mins to release the whole shop if there was a problem?