His art collection appreciated greatly over a period of thirty years.
I am wondering the reason why the verb appreciate has not been used as following:
It would be appreciated...
Thanks in advance
Appreciate has both transitive and intransitive uses.
As a transitive verb (which is required if you cast the sentence in the passive voice, be appreciated, as in your rewrite) it has a range of meanings: 'value, recognize or assess the value of, be grateful for'.
As in intransitive verb (which is how it is used in your first example) it means 'increase in value'.
His art collection appreciated greatly means the value of his collection increased.