Thank you for the praise in the first paragraph.
The reason I used space didn't really exist, I just rest my finger on it a lot of times and decided to use it ¯\_(ツ)_/¯
As for the WASD and Space for the menus, it is to comply with the game jam rules for the jam this game was made for: GB30. One of the minimum requirements was:
- Four directional inputs, two "action" buttons (A, B), and two "menu" buttons (Start, Select)
So a mouse system would have been a wee bit cheating. As for the exit button, you are correct, it is for the desktop version.
Finally, the 'select' instead of the 'move-the-cursor system' would in fact be better, but I didn't have time to implement it.