Sorry, but this is absolutely not odd You don't have any idea, what odd things people are collecting! To collect and complete book-series, is something totally usual.

I was a collector all my life, but I was able to reduce and specify them. You can call it "collection" only, when there's a structure in it. With a wild cluttering you are only a hoarder (The German word is borrowed/selfmade from English: "Messie"), but not a collector.

When I was a small boy, I collected post-stamps, but not really intensive. Then WIKING-cars along the 80ies, but when I got my first real car, I stopped that (plus the fact, that WIKING-cars became to expensive). License plates I've also collected since I was a grammar school-boy, also other car-stuff, literature - and car parts. As hubcaps, I've found on the street or parts, neighbours gave me, who had worked on the cars in the backyard.
Ah yes, and crown corks. But for those I never had spent money. I just kept and picked up those, which are around me.

Later on I reduced my collecting accurately. No WIKING-cars any more. Those, I already had, stayed in their showcases, but none new any more. Plates only originals from disappeared West German counties, and the car-stuff I've strictly reduced on K 70-related things.

Everything, which doesn't belong to the systematics, I gave away or I've sold, since 2001 via eBay.

@Antoine: when you are doing eBay, then you will see, what for stuff people are collecting. I had known crazy collectors long before, but in the last 12 years with eBay, I've made many more strange and funny experiences
Especially due the fact, that I've offered everything via eBay, not only collectibles. From tiny things as crown corks -once even an old, used plastic bag (from BÜSSING-spare-parts)- up to complete cars (my wife' Astra G, my dad's Passat Variant 35i, mother-in-law's 1996 Escort Turnier and a wreck of a 1937 DKW F7, everything went out via eBay.
When my grandmothers and my wife's grandfather died, I've put the most usable household-stuff at eBay. Sure, it was a plenty of work, for months, but it made fun. It's nice to see, how other people became happy with your old stuff.

And carefully made eBaying is educational, too. When you look and search, what an item you have, and if there are collectors for that, you pimp your education-level