We’re not doing more levels right now, because the priority is on increasing the replayability of the current levels. New difficulty settings on existing levels are easier to implement and avoid the following “downsides” of new levels:

• Making new levels takes a long time - laying it out, testing, repeat. We’ve got about 11 “rejected levels” that didn’t make the cut.
• Each new level adds about 1mb to the build size
• New levels aren’t as replayable as old levels (!). It’s fun to get to know the layout and deal with the enemies.