In my personal life it's hard to spend bitcoin when not a lot of merchants accept bitcoin in the first place... I try to use bitcoin as payment as much as I can but sometimes this is just not possible. Some people maybe saving and storing their money in bitcoin as an investment and for their future.
I don't think it really matters what people do with their bitcoins, whether they store it, invest it or spend it is totally up to them. That does not destroy the Network at all!