Theatrhythm Final Bar Line devs address touch control absence.
The developers of Theatrhythm Final Bar Line, Masanobu Suzui and Ichiro Hazama, explained in a recent interview that the decision to exclude touch controls from the game was due to the difficulty in preparing sheet music that was fun to play with both touch and button controls, as well as the fact that the Switch has a capacitance-type touchscreen while the 3DS had a pressure-type one. The team ultimately decided to specialize in button controls for each song.