It seems a bit of a stretch to say that "the things that make good games are arbitrary".
I have played a lot of games in my time, good and bad.
It's not too difficult to identify reasons that some games are better than others. Design and balance is pretty important, if a game feels "unfair" in some way for example or doesn't feel responsive and leaves me feeling detached from what is going on then I'm less likely to play it for long.
It's easy enough to "clone" a game, but even building something like a simple tower defence clone involves making a ton of decisions that affect playability quite a lot.
I have played a lot of games in my time, good and bad. It's not too difficult to identify reasons that some games are better than others. Design and balance is pretty important, if a game feels "unfair" in some way for example or doesn't feel responsive and leaves me feeling detached from what is going on then I'm less likely to play it for long.
It's easy enough to "clone" a game, but even building something like a simple tower defence clone involves making a ton of decisions that affect playability quite a lot.