Over and over what kept occuring is once the Japanese were flushed from their caves/hills and other cover, they became easy targets because of the tactics they used, mainly taking all their men and running bonzai charges. They literally became sitting ducks for our boys. They tended to take platoons, companies, etc. and run full-out charges regardless of terrain and odds. So many Japanese troops were needlessly slaughtered. Top that off with their fight-tiil-were-all-dead/we ain't gonna surrender beliefs and well you wind up with really high atttrition rates.
Of course our boys also suffered high attrition rates because the Japanese did not believe in surrender. It was an utter disgrace to them, and hence many battles that should have ended much sooner and would have saved many lives on both sides...
As you probably know, but maybe some that are reading this do not, is that many Japanese troops jumped off cliffs, etc., taking their own lives, rather then surrending to the Americans. IIt was literally fight-to-the-death. They were also told that Americans were animals and would do horrible things to them if they were captured. Ya, look what the hell they did to our boys throughout the war. Look at the Bataan Death March. There are hundreds of other such examples. 
Proud Daughter of Walter (Monday) Poniedzialek
540th Engineer Combat Regiment, 2833rd Bn, H&S Co, 4th Platoon
There's "No Bridge Too Far"