Can someone explain why I didn't pass this level?

Oops, your screenshot really does show how rigged this game is @SarahSD !

I have seen many players complain about seeing unmatched triplets of candies on their finishing failure screen, but that can usually be put down to the final cascade cutting out short. The three dragons over their exits prove to me that the game determines if we will pass or fail in those last two or three moves, it is written into the game and if we are on a "fail" board then fail it will be regardless of what the player does. A glitch like what you see in your game demonstrates this: Those dragons simply were not meant to come down because you were assigned a "fail" board, but there was obviously an error or glitch in the coding for the final cascade which did bring the dragons down and the game did not recognise this because it was set to "fail".

So what you should do here is complain to Player Support directly via Settings in your game. Go into settings (the small pink cogwheel) and then click on the ? icon and scroll through the options until you see "contact us" at the bottom. You will get an automated answer at first and if you don't get a satisfactory follow up response, reply to the automated message and send your screenshot. The least that Player Support can do is to add 10 gold bars to your account so you can pass this rigged level at your next attempt.