Several reasons:
1 - The main reason I found this site - my Phillies collection - I wanted to see what I was missing from the years/sets I had cards. TCDB helped me know what I was missing, and helped me be able to fill those gaps.
2 - I was able to add those cards to my want list and was able to track the progress I was making toward completing some of those years.
3 - I found a couple cards listed with the Phillies that should have been other teams and I found some cards in my collection for the Phillies that did not have teams listed. I submitted an inaccuracy report on those, and I was greeted with a message back stating "You could make that update on your own, if you want to." Oh, wow. I could do it and not bother the site Administration about this? Cool! So I started making edits to fix the Phillies cards. And then I started making edits for entire baseball sets I had (or had some crds from). Then I also made some edits for the hockey sets I have. Then I saw the "Missing Abbreviation Descriptions" page, and with the help of only a few other members, we knocked that down to "maintenance mode" (where in December of 2015, well after I started working on them they were sitting at more than 14,000 entries were missing descriptions to zero by September 2016). After that, I joined forces with 3 other members and we devised the Rules & Guidelines document (culling info from the FAQ, forum posts, and messages with Admin). It was shortly after that when Admin opened up the Inaccuracy Requests (IRs) to the membership. It quickly became my "home". I enjoy the feeling of fixing problems with the site. I wish there were less problems, and that's where I send messages out to members trying to get them to understand the rules/guidelines/policies of TCDB as a means of educating. (I'm still working on getting the wording right so the tone of a written message comes across as helpful and not scolding.)
4 - The other members of this fine community. I have met 8 in person, which included trades, meeting them at a card shop, or just being social. I have also traded with several (on and off the transcation manager) and have even spoken with one over the computer as I showed him how to handle a certain type of site issue. I have always said that most of the people in the card hobby are the best people in the world, and the community here is the best of the hobby. So basically, TCDB is the best of the best.
5 - Admin himself. Yes, having dealt with him a lot (more than he probably wishes, however, it's helped take a lot off his plate), I really appreciate all he does for this site, the hobby, and the members here. Also, he's just a genuinely nice person. He enjoys his anonymity, and I respect it. It's because of his disposition that I keep working on the site and the IRs (and other things that I see that are incorrect and can fix without getting him involved).
You asked, Jonathon!
-- Dan --
Note: Please see my profile for more info regarding trading (section updated 3/4/2024). I have added a large portion of my inventory to the site, and currently have trading turned on (details are in my profile).