I had the same rant against a few apparently joystick-only games. Or games where the keys seemed awkward and non-configurable.
I agree with you. Although the CPC supports 2 (3 according to hardware schematics?) fire buttons, the official fragile Amstrad Joystick has only one. And my joystick was broken. A game assuming two buttons are available is a bet. IIRC a number of games allow some key alternative (play with joystick, one key for second button).
For best player satisfaction I tried to make Just Get 9 maximally playable while keeping it simple: use either joystick or cursor keys or any combination of a preprogrammed set diamond-shaped or one-hand-horizontal one-hand vertical key sets. Also “action” can be via a fire button or copy or space bar or enter plus a few others. Secondary (open menu) is second fire button or Esc or P (for the GX-4000). Plus a few others like F which is the second fire button of the second joystick.
Oh, and given thay all keyboards are not QWERTY (some AZERTY or QWERTZ) I do not use AZQWM keys. This eliminates the awful WASD combo which says to the world “this author has never used a non-QWERTY keyboard”. This affects even more nowadays that emulators add an extra layer, with confusion between emulated CPC ROM, positional or symbolic keys policy, emulator being confused about what the host operating system knows about the hardware keyboard, not even talking about using all this from a remote machine. Robust key choices always just work without anyone noticing. Launch and play.
See the README in the download on Just Get 9 by cpcitor for the details about keys (or just try the keys, there are small surprises to discover 
).