What did the General commanding Japanese troops on Iwo Jima do differently that cost so many American lives ? As compared to other island battles?

I know they were heavily dug into Mt.Suribachi with tunnels that allowed them to shift positions. I think they also had clear sights of the landing zone.

The Japanese chose not to oppose the landings themselves but instead took on the American invaders from heavily fortified and defended positions inland. (They were still always going to lose though, they just hoped that inflicting heavy losses on the US might prevent an attack on the "home islands" by the Allies.) As it happened, the war took an altogether different course anyway.

The japanese waited till americans got on shore and they were having a field day with our troops