Why Orochimaru tries to steal other people's bodies instead of just reincarnating into his own offspring?
Simply using bodies identical to his own would run counter to his obsession to learn every jutsu there is.

Consider two of his potential hosts that we saw in the series Kimmimaro and Sasuke. 

Kimmimaro was the last of the Kaguya clan and the only person left with the ability to use bone techniques making him the only chance for Orochimaru to acquire them though Kimmimaro's terminal illness ultimately made him unsuitable.

Then we have Sasuke stemming from his desire to obtain Sharingan and their ability to copy jutsu on sight which would allow him to easily expand his repertoire.