The answer probably best lies in the rationalization for the attack in the first place - to cripple American ability to project force in the Pacific.

The attack was intended to sink or damage the entire U.S. Pacific fleet in a single maneuver and was only partially successful to that end. While the loss of several U.S. battleships was a huge blow to American power in the region, the attack failed in its main objective of sinking the U.S. Pacific aircraft carriers, which were deployed to sea at the time of the attack.

In addition, the attacking Japanese fleet was operating towards the extreme range of their capabilities when they struck at Pearl. While it is possible that fleet could have proceeded to attack the U.S. West coast, they would open themselves to much greater risk - including the possibility they would never return. Such a blow to the mainland could have a psychological impact on the United States, but would not serve to limit the ability of the U.S. to fight in the Pacific.

Had the attack on Pearl fulfilled all of its intended objectives, it could have taken the U.S. years to rebuild their naval capabilities in the Pacific. Or it would require part of the U.S. Atlantic fleet to be detached to the Pacific which would also take time (not to mention a reduced fleet theoretically could be destroyed with greater ease in subsequent engagements).

Japanese policy in the Pacific leading up to the attack on Pearl Harbor mostly involved regional expansion, but was limited by their supplies of war materiel - most importantly oil. American policy before the outbreak of hostilities revolved around limiting the amount of this basic requirement through embargo and political influence on Japan's neighbors.

With the destruction of the Pacific fleet, the United States theoretically could not back up its stranglehold on the commodity, and could thus not limit Japanese military expansion. A main purpose of the attack on Pearl was to buy time for the shoring up of newly acquired Japanese holdings, most importantly securing a protected source of petroleum.

As a side note, there were Japanese attacks on the mainland U.S., most famously through the use of "balloon bombs." These were gas filled balloons supporting a bomb payload released into the trans-Pacific air currents, designed to float across the ocean and release their payload over the American west coast. The impact of such devices was mostly psychological (and they were sort of effective at this end, and did end up killing a few folks), with the secondary purpose of starting forest fires in the timber rich American north-west.