Perhaps it's because its is not commonly usually used as a pronoun. In contrast, his is.
In the Oxford Dictionaries Online, his is listed as both a possessive determiner and as a stand alone possessive pronoun. However, its is only listed as a possessive determiner.
However, Collins English version also limits its to a determiner, but its American version lists both pronoun and determiner.
Several other dictionaries consulted, such as American Heritage, limit its to adjectival or determiner use, but a few do list it as a pronoun.
The other possessive pronouns differ from their possessive determiner forms:
In sum, it's technically correct, but a bit off sounding because it's uncommon.