Because I might use them one day.
That's the big problem with the reuse part of reduce, reuse, recycle. I have a house full of things I am going to use one day. I have a wall full of fabric and the last time i used the sewing machine was perhaps nine years ago. I have, however, made two quilts from stuff in the baskets. (I am a Virgo, albeit a very lazy one, so all my fabric scraps are sorted by color).
It's not just toilet rolls and fabric. I have a house full of things I am going to use one day. And every so often I do. The toilet rolls make rather good planters for trees from seed. Corks? Not bad as place name holders (or should that be name place holders? Anyway, the way to show people where they should sit at the dinner table).
Reuse can be a lot of fun. Ask yourself "how could I use this?" before you chuck it in the garbage bin. Upcycling can be a lot of fun. The internet is packed with loads of ideas for turning jeans into planters, or books into lamps. What bothers me is that many of the pictures one sees on Pinterest are clearly newly purchased jeans. That is not the idea at all. The idea is repurposing. Don't chuck old tee-shirts; turn them into cleaning rags. Don't chuck - or recycle - glass bottles; channel the 70s and cut them off to make drinking glasses, or lamps, or wind chimes.
Use your imagination. Just don't throw some thing away until you have seriously considered whether it might have another life.