what cause low saving rates?

I think a lot of it is attitude. If people have the attitude that nothing will change, and that they are entitled to have everything NOW, then they don't save (or invest) for the future. I'm not sure where this cultural attitude came from, maybe from the internet which is a somewhat distorted reality.

It has less to do with the amount of money people actually have. In the Great Depression, people made do with much less, used up food instead of throwing it away when it was marginal, patched their clothes and other belongings. They saved all kinds of things, not just money.

Assuming you mean the amount being saved and not interest rate, having a low income and alot of expenses doesn't leave you much room to save. If you mean interest rate, then supply and demand. If there is a lot of money available and few people asking for loans the interest rate drops. If there is only a little money available and a lot of demand for loans, the interest rate goes up.