I would like to know why it's ok to say
* It is easy for the wooden houses in Japan to catch fire.
* wooden houses in Japan catch fire easily.
but wrong to say
* Wooden houses in Japan are easy to catch fire.
please help me, I would really appreciate it!!
When you say "something is easy to something," you are really saying "something is easy for you to something." (Or "for one.")
"English is easy to learn" means "English is easy for you to learn."
So with this the clause in your sentence becomes "Wooden houses in Japan are easy for you to catch fire."
But that doesn't make any sense, since "catching fire" is intransitive. It doesn't take an object. Something catches fire. Someone doesn't catch fire to some other object.
Now, if we add one preposition, we can make a valid sentence, but with a different meaning.
"Wooden houses in Japan are easy (for you) to catch on fire."
That means that you can deliberately set them on fire pretty easily.
But that is not the meaning you intend.