We hang on to stuff for all sorts of reasons (and often not really knowing why). Possessions can offer comfort and security; our identity is often closely associated with our belongings.
Sometimes we think that because we have paid for something, we shouldn’t throw it because we’ll feel guilty. Or we will lose information, which might lead to feeling a lack of control. If we hoard, it means we can put off the decision to discard, and the worry that comes with that decision (ie the worry that you might make a mistake).