为什么“goodshape”前面不用加“a”？

不是一般不可数名词被形容词修饰后就要当可数名词了吗？

good shape 良形; 精神或身体状态好;

The players tried to keep themselves in good shape .
运动员们努力保持良好的竞技状态。
But always is good be in good shape or play against some players behind you.
当然，保持良好的状态或者对阵排位比你低的选手，也总是不错的。
Keep your credit rating in good shape. A poor credit rating leads to higher premiums.
保持你的信用评级良好。穷人的信用评级导致较高的保险费。

加不加A，主要看意义是否具体或抽像。

具体的意义，多加a.

good shape 良形; 精神或身体状态好; 比较抽象。

搜一下：为什么“good shape”前面不用加“a”？