English speakers use the possessive apostrophe ("someone's something") where possible, because it makes sentences more clear to specify a direct object without it also being the object of a prepositional phrase, and it makes nested ownership more clear. Consider the sentence:
The toy of the cat of my sister.
This is technically correct. It has eight words, two prepositional phrases, and it's a nested ownership - my sister has a cat, and that cat has a collar. Furthermore, the nested ownership is listed in a pretty unnatural order - from most specific (this one toy) to least specific (things my sister owns). It's more concise and understandable to say:
My sister's cat's toy.
In my opinion, this is a lot more concise (4 words, no prepositional phrases) and the nested ownership is listed from the least specific (things my sister owns) to the most specific (this one collar), as you would expect from an outline: