My mom is almost entirely unable to throw things away. As a consequence, my parents have boxes and boxes of all kinds of stuff stored, including some of my toys

My mom is almost entirely unable to throw things away. As a consequence, my parents have boxes and boxes of all kinds of stuff stored, including some of my toys from 20+ years ago. They live in a rather big house, but it is starting to encroach on their living space, and it does prevent them from using some of their extra rooms for their original intent, such as a dedicated washing room, so they could move the washer/dryer out of their downstairs bathroom. Every time my dad and I try to bring up the subject of clearing all of that stuff away, she counters with claims like "but that's our winter clothes" or "as soon as I have the time", which never happens. I've talked to her about why she tends to accumulate stuff like that, and she thinks it's because her family didn't have much when she was growing up, and her mother was a semi-functioning alcoholic. She says they often experienced simply running out of basic things, and couldn't immediately afford to replace it. So she internalized a need to keep everything around, never throw out or give away anything that still works, and always have at least one spare in storage. They have three refrigerators (for three adults, my sister still lives at home), which are all stuffed full at all times. This leads to ~monthly rituals of cleaning out all the spoiled food, and then filling up the fridges again to repeat the cycle. When questioned on this behavior, my mom argues that they need to keep all the different spreads and stuff around at all times, because you never know what people might want to eat. We try to argue that it's perfectly OK to not have every single food you would possibly like to eat at any time available at all times, but she doesn't seem to want to agree.