When you have a parent who collects things and can’t or won’t get rid of any of them even when it endangers their safety, you wonder why they behave this way. There are several thought processes that may be at work here.
If your mother keeps everything, then she can avoid the anxiety of making a decision. She’s thinking “what if I throw this out and I need it some day”.
She may have developed extreme emotional attachments to her things. Her things are more like extensions of herself. If she was to get rid of the item it would be like letting go of a part of herself. Her things re-enforce her identity. You may not value the little dress she made for you when you were eight years old, but for her it is a reminder of when she was young and vital and needed.
She might have trouble with categorizing. You, as a non-hoarder, see similarities and can group items together. Your mother, however, sees only the ways things are different and baffles you with the ways she creates piles of paperwork and other things that make no sense to anyone else.
So, what can you do? Start by listening. Engage your parent in a discussion where you listen more than talk. Let your mom tell you the history of the items and what she thinks she might do with them someday. Just let her talk without offering your own evaluations. You are creating a relationship hopefully based on trust.