The current trend is to make games ever more concrete, but we must not forget abstraction. Generally speaking, abstract games challenge deduction, while concrete ones challenge induction. Put another way, games with lots of specific rules and solid metaphors force the player to form their own generalizations and strategies, while games with a few simple rules and few examples force the player to devise effective applications and tactics.

It is harder to make abstract games than concrete ones. Good abstract games, anyway. It’s actually easier to make concrete ones, but they are usually mostly rubbish (though it may take a while for people to figure this out).
Abstract games are easier to critique because the conclusions can be tested. Concrete can be defended by multitude of examples, while dismissing abstract conclusions.
Abstract games are less distracting, and thus flaws stand out more, plus elegance is harder to perfect than bulk.
One can take examples from real life when creating concrete games, wheras one must turn to philosophy for abstract concepts.

Why abstract? Abstraction has advantages of its own.
Abstraction is emergent. If the concept results in many useful concrete examples, you have emergent behavior.
Abstraction is compact. An abstraction is simple and concise. It is elegant, transportable, and pure.
Abstraction allows the codification of formative principals, which seem to be critical in intelligence (natural or artificial).
Abstraction is very important for automation, planning, and communication.

The abstract, as well as the concrete, is necessary for a believable experience.