Here is my personal reason(s) for collecting:
I should note, to start, my interests change periodically. They come and go in 2-5 year spurts usually. There is retained interest in all of my hobbies/collections, but primary interests fluctuate.
On to the reason(s):
Simply put, I enjoy collecting. The thrill of acquisition, the fun of researching/learning about the acquisitions, the time it takes to care for the collections, and sharing collections with others.
I get bored quite easily. I have sporadic insomnia. I like having multiple things to entertain me and to do, such as collecting, reading/learning, projects and/or organization. It is highly interesting to see technological progression (or regression in some cases) of the items in the collection. I like diversity in stuff I collect. Any quality and/or interesting tool is of interest and usefulness. This is why I don't get into brand fandom.
Things I've collected that aren't multitools/knives/saks/measuring devices/etc:
Small motors. Briggs, Clinton, Tecumseh, Robbins, etc. A lot of these have been traded and sold, because of my big move in 2011.
Vintage portable computers. TI PPC, Compaq Portable I/II/III, Kaypro, Osborne, IBM, Tandy, etc.
Custom case high-performance PC gear Benchmarking, Overclocking, modding, local-custom competition, etc.
Vintage transistor radios and vintage calculators. This collection never got tona significant level, but it is diverse.
Watches. See watch sub-forum for images of current watch collection.
Cameras. TLRs, SLRs, Range Finders, Bellows cameras, and miniature spy cameras. I did sell some if this collection for my 2011 move, but a significant number still reside in storage.
Vintage telephones. Western Electic, ITT Kellogg, Signal Corps, Stromberg Carlson, etc. Most of the vintage phones are 1930s-1970s rotary dial.
Coins. Mostly silver antiqur U.S. currency.
Clocks. Not a large collection, but does include a few early/mid 1800s examples and many art-deco style windup and electric clocks.
Vintage Stereo gear. Altec Lansing, JBL, Sansui, Pioneer, Kenwood, etc. I sold my dream system for that 2011 move; which consisted of a Pioneer Spec-1 and Spec-2 Amp/PreAmp (200+ wpc), CT-F9191 cassette, PL-530 TT, RT 800 R2R, and matching tuner(forgot model..err).
Yeah. I'm nuts, but I thoroughly enjoy collecting and it doesn't negatively affect anything in my life, aside from my spare cash.
Reading is another interest of mine(I know my poor typing skills make this hard to believe, but nearly everything I write on MT.o is done on my cell phone, so please cut me some slack..haha).
Most of what I read (books and articles); Science, Science-Fiction, History, philosophy, and anything else thay interests me at the time. Though, admittedly, I am not what I would consider to be an expert on these topics.
When I read the psychological article I posted, I don't apply anything after enjoyment as a reason, for myself. I found the S.F. reference hilarious to be honest. I was thinking to myself that, using his reasoning, we should be collecting bags of our own waste.
I hope this post sheds some light on the scope of the collector personality and the manifestation, in my personal case, involving collecting.
Sorry to anyone who feels they wasted several minutes of their day reading my brain poo.