They did. A lot of Japanese-occupied islands were indeed bypassed. The fleet anchorage at Truk, for instance; it played host to a significant portion of the Japanese Kaigun and saw only air raids. By 1945 Truk was so irrelevant that the British Pacific Fleet used it as a trial run for some of their carriers on 1945 June 14-15. Rabaul, one of the strongest Japanese fortifications, also saw no invasion.

I commend to your attention the following previous threads:

• u/wotan_weevil and u/kieslowskifan address just this same question;
• wotan_weevil has some further thoughts here;
• and u/jschooltiger provides a high-level overview.

And we still welcome further contributions from other users, so if you'd like to put in your own oar about island-hopping, please don't let this post stop you!