My reason is fairly simple, it doesn't allow you access to the classifieds. If it did I'd pay up today, and pay much more than the standard fee.
I love ECF, and would love to be a supporting member, but personally find it a bit of an offense that even if I pay money out of my pocket, I'm still not able to buy and sell with the rest of ECF. I refuse to use eBay or PayPal due to personal experiences with both of them in the past, I think they are a terrible company and haves some serious moral issues with their actions. I'm not singing back up on either site just to buy and sell here on ECF. Having no access to the classifieds obviously I've never bought or sold anything here, so nobody can "vouch" for me to get into the classifieds. Catch 22 if I ever heard one. The NetID thing is out of the window for personal reasons.
So, I figured, no need to fear, I'm sure being a supporting member means you have access to the classifieds, which evidently isn't the case.
I totally understand the reason for having checks in place to help stop scammers. I was a member of a forum that had "secret" classifieds (***) sections that weren't allowed to be spoken of in the public forum, as is an invite only deal. Unless several people in the know nominated you, and you were let in, you wouldn't even know there was a classifieds. Even with this level of care, there were still scammers, I was had for about 600 bucks by a long-time, highly respected member of the community. He scammed about 20 other people at the same time too.
Now I'm starting to ramble, but overall my feelings are this: I've been here close to 2 years, have never caused trouble (AFAIK) and have done my absolute best to be a contributing member who helps his fellow vapers whenever possible. I'd like to help out financially as well, and would, but it just feels like too much of a slap in the face for me. I understand the need for the rule, sometimes people fall thought the cracks and just can't meet certain requirements, and that's OK, but that doesn't mean those people have to be happy about it.
After reading this post I realized it came off a bit... hostile? I just wanted to make clear that I'm not attacking ECF or it's policies, just explaining my personal reasons for not being a supporting member. No ill will towards ECF coming from me.