Here's why:

* Sediment is the solid material that settles to the bottom of a liquid due to gravity. This material is typically insoluble in the liquid.

* Precipitate is also used for the solid that forms from a solution, but it usually refers to a chemical reaction where a substance becomes insoluble and settles out.

So, while both words can refer to the solid material at the bottom, "sediment" is a more general term for any insoluble material that settles, while "precipitate" is specific to a reaction-driven process.