Why are there different content policies on different sites?

For example: homework-like questions are strongly discouraged on [Physics][1] and are immediately put on hold. Such questions however are asked a lot in [Mathematics][2] and are quickly answered. Why is there such a different content policy on the different sites?

Are the content policies standardized for all sites or are they decided by the site moderators?


  [1]: https://physics.stackexchange.com/
  [2]: https://math.stackexchange.com/