They can be, goof2658, but Japan has the option of moving two of its carriers over to Tokyo Bay on J1, and up to four fighters can land there after the Pearl Harbor / San Diego J1 attacks. That’s plenty of protection against one bomber.
So, if you want to maximize your attack on Asia, rather than your attack on the US Pacific navy, you can kind of stack up near Tokyo instead of stacking in the Caroline Islands. Depending on how many of your fighters survived, this is often a good idea anyway, because your stack may not be safe in the Carolines.