It’s to hopefully get them to shift any normal defenses west first, leaving less in the east. The idea of being on Hawaii could cause America to shift defenses to WUS for a landing at San Fran. No matter how you land, America can obviously build 10 infantry, but putting yourself in position to attack either coast always gives you the option of attacking the weaker one.
Being on Hawaii normally doesn’t cause America to buy 30 infantry, 10 on each. They’ll simply try to buff up Western. On Japan you move to SZ64, America moves what it can to Central (too many tanks to EUS means no go usually), then on Japan’s next turn you take EUS and grab the cash and promptly get crushed by the counter attack. Never said it was a good plan, but taking America is probably “bizarre attacK”.
You’re probably always going to be facing 30 infantry in America at some point if you try to take it. Again, taking out America doesn’t really happen anyway, but if you’re set on trying, might as well go for taking the IPC.