We made the intentional choice for the bosses to restart you from a menu in the event that you failed. Traditionally, that's how the boss rush genre has worked. That's why we added in the boss select to face off against bosses that you've at least seen in order to spend time on them to learn.
We considered a tutorial but figured that our time would be better spent on a control description on the front page and finishing a third boss.
Thanks for taking the time to check out our game!