We usually use 'than' when we compare two objects or people directly :
My camera is better than your camera (or, than yours).
But we usually use 'than that of'/ 'than those of' when we compare not the objects but the attributes or qualities of those objects :
The colour of my camera is brighter than that of yours. (= than the colour of your camera).
Here, 'that' stands for 'the colour'. Here, 'that' has been used to avoid the repetition of the noun 'the colour'.
Besides, a possessive pronoun expresses "the possessor + the thing (s) possessed" (from the context) :
"His net worth is more than Bill Gates's." (Bill Gates's = Bill Gates's net worth).
You could also say :
"His net worth is more than that (=the worth) of Bill Gates." (You need not use double possessive here.)
"The camera on this phone is better than yours." (yours = your camera).
It's better to say :
"The camera on this phone is better than that (= the camera) of yours (= your phone)."
"The camera on this phone is better than the one (= the camera) on yours (=your phone)."
The pronoun 'one' is also used to avoid repetition of the noun.