They are addicts to credit cards or like them for perks or have been building their credit through the years and slowly grow into more rewarding and "prestigious" cards. Some, as you mentioned, might also do it to falsely lower their util %. I suspect for the non addicts it's mainly because they are growing their portfolio into better cards and don't want to close oldies so they "sock drawer" them.
I am guilty. I have 25 now. 
With a potential 3 more coming that I thought were outright denials, and probably will be. I have 7 that I need to kill of. I app'd before I knew any better. Then I learned and app'd again for better cards. Now I am in the garden until the dinosaurs come back.
@Septrosh wrote:They are addicts to credit cards or like them for perks or have been building their credit through the years and slowly grow into more rewarding and "prestigious" cards. Some, as you mentioned, might also do it to falsely lower their util %. I suspect for the non addicts it's mainly because they are growing their portfolio into better cards and don't want to close oldies so they "sock drawer" them.
I take back what I said, this sounds much better. I want to go with this answer instead. 
Good info guys, thanks. Differing reasons. And as always, thanks for the subtle passive aggressive response Irish80 
Those of you that have so many cards, did you pick them up a few here and there over time or go on massive app sprees a couple of times? I imagine answers differ to that question as well.
@Anonymous wrote:I've only been on this forum for about a week and have really been enjoying all of the reading material. One question though which seems adequate to ask in the credit cards section here. Why do so many people on here have so many cards? I look at some of the sigs and see 10, 15, 20+ cards. One of the points that seems to come up in a lot of FAQs and such is basically if you aren't going to use it much or don't need it why get it which seems sort of contradictary to a lot of what I see on here. I mean maybe some people have the cash flow to be using 15-20 cards a lot each month, but I would think most dont. I undestand that it certainly keeps your utilization % super low and all which is certainly a benefit, but what are the other reasons for having a near half deck of cards?
How many cards do you have?
For myself, there's several of the cards that I've had a long time, including with high utilization and high balances. As those balances came down, in 2013 I started to notice the possibility of getting rewards. After joining here in late 2014, the specific rewards possibilities were easier to find out about due to the conversations of the members. The sign up bonuses for travel type cards, business travel alignment I have with some of the loyalty programs, and the ability to actually get approved for new cards now that my balances are down, leads to the situation where I have 25 active and reporting open cards The annual fees will be a reason to close some, but not all of the cards. The no AF cards often have other interesting features to keep them active.
The other consideration is, you can app for cards because they are there. Handling credit is a skill, the offerings of the banks are looking for good risks to issue cards to, and so taking the bank up on their offer gives you a chance to see whether the card works for your spend, whether you like the reward structure, or not. People can get as many cards as the are comfortable handling, bounded by the willingness of the bank to grant the credit.
In the long run, it's only one more financial relationship that one has to manage, and so each person makes their own choices how much they want to try for.
@Anonymous wrote:When you first join this forum you can get bit by the bug and go a little app crazy for really cool cards that can do "cool" things. For some the itch never stops and for others once they get it out of their system, they try to cut back and strengthen their cards to have what they only need / find useful. Regardless, if you're responsible none of it is wrong, credit cards are out there for people to use - whether it be for Low APR, Sign-Up Bonuses, Rewards etc.
I like this one too. It makes me seem like I might be responsible. I'm not, but for a minute, I thought there might be hope.