I’m with at @syz: it’s just something cats do. If you want an animal that you can understand get a fish or a pet rat or a dog, even.
I was living with my two cats in my parents’ house when my dad was installing and repairing computers for the school district. He had a workroom upstairs and for about a year and a half … we lived in a Cape Cod, so the bedrooms were downstairs, my cats would bring miscellaneous stuff down from my dad’s workroom and deposit it at the end of the hall between my bedroom and my parents’ bedroom: little jumper cables, small tools like the smaller screw drivers, hex wrenches, packs of button batteries, USB cables, miscellaneous stuff… and one of us would collect it all in the morning and return it to the workroom and they would bring it all back downstairs the next night.
We tried to figure out what was motivating them, to no avail. It was all pretty amusing until one night, along with the rest of the usual haul, they brought down the small portable butane soldering iron, a spool of solder and the motor from one of my dad’s remote control helicopters that he was repairing. That had us a little worried. :-) That made it seem like they had a real plan; they were up to something, no doubt, we just didn’t know what.
But they just stopped doing it after a while. Either they just got tired of it or they realized that we would continue to thwart their master plan, whatever it might have been, by taking everything back upstairs every day. Cats are mysterious creatures. You can waste a lot of time trying to figure them out and end up no wiser than you began. Just enjoy the mystery.