It isn't necessarily a trivial problem to solve either. Retrofitting a touch interface on to a game designed to be played with physical buttons doesn't always work out well.
Absolutely on the money here. I finished it for Desktop and was thinking of making it Mobile friendly, so I started reading on it and realized I designed myself into a corner because of support for touch interfaces. Learned that lesson. The simple solution would have been 4 buttons at the bottom of the page, but just wasn't as nice playing on mobile that way.
I haven't checked the App/Play stores for Tetris-like games, so I'm sure that my suggestion to override the volume button as the rotate button in Tetris is probably old-hat. If it's not, then perhaps this is the key (excuse the pun) to providing it to the mobile world. Note, that the touch screen would be required to move the blocks left-right and accelerate down.
How difficult it is to add the virtual keyboard with 4 keys