Minimalism (not needing a massive house to store stuff in does make life cheaper on a variety of fronts), "he who dies with the most tools wins", "that would have been so useful on the last 5 occasions", "this would be useful when this task I could be asked to solve comes up*", desire to preserve things (some might also want to be legit if it is games and other intellectual property but eh, still you own those GBA games now so guess the ROMs you had for the last 15 years are legit after a fashion), desire to impress your clone if they popped into existence**, potentially some kind of investment*** and more all war within myself.
*have I needed a network/phone cable punchdown tool in the last 10 years? No. Network cable crimp tool hundreds of times though. If your network fixer does not have a punchdown tool though then something is a bit wrong so I have one. Repeat that a few hundred times for other tasks I find myself in the field of sorting and yeah some effectively redundant tools creep in.
**nobody really cares about my books (or if they do it is more likely that I rammed the information in them into my head and what that can do for them and they indicate that) and most of my games. I like them though.
***I ended up with a very shiny N64 collection (granted 99% PAL) because the N64 was a failure and things were going for pocket money, same for a variety of other things that I go in for in games. Left it in a box and today it is apparently worth a bit. Have not checked recently but going by prices of things in related categories when debating just going on online tat merchants for the things on my list my xbox, gamecube, wii, xbox 360, NES and such collection is probably worth more than the rock bottom prices I put into it. Whether such things would be worth more than had I invested it in some kind of stock index at the same rate... indeed whether having it in a high interest savings account (likely well below inflation though) would have done better is a debate in some cases.
In my case preservation is my main goal for me. I really distrust downloadable setups I can't trade games out on (even ignoring "delisting" not like we have not had several dozen DRM encumbered services, including from big players, go down already or do strange things --
https://www.theregister.com/2009/07/18/amazon_removes_1984_from_kindle/ ). Library of good games and history of development of certain styles and mechanics in games that might not be all that good being my general focus in such things. Books both because I dislike some of the effective book burning that is ramping up (I consider most revisionist efforts this), and because some and science/tech/engineering actually are in a bit of danger of popping out of existence which would be a shame at some level. My DVD collection is some combo of the two there (this cutting scenes to comply with current fleeting social concepts of what is righteous... ew) but far less serious.