Comment by Nfsaavedra

Glad you asked, as the answer is, in my opinion, interesting. Developing a game like this seems pretty simple until you have to make a UI that fits on a phone. If you look at the default keyboard on your phone, you will see the suggestion bar or something similar. When space is limited, that space is crucial, and that extra height is enough for a row in the game.

Another benefit of having our own keyboard is that we can remove language-specific characters that may not be handled well by the game's daily functions.