A comment the devs made on the steam announcement (under slay the spire) regarding someone being angry that this was prioritized over slay the spire 2:

Hi there, this is just a small, free game we made in a few weeks for a game jam in order to get acquainted with the engine that our next big game is currently being ported to. We figured our fans would be interested in knowing what we're up to as we work on our upcoming title since switching from Unity has extended its development time.

We're currently back to work on our next big game, this time refreshed and with lots of new tools under our belt! Hope people have a fun time trying this out if they'd like to!

So it's not like this is a big new genre for them, but it's also not meant to be a commercial for Godot.