I've backed three successful campaigns. I'm currently backing 12 other campaigns.
My first two campaigns, I backed because I happened to know the owner - he's the current owner of the company that I'm looking to take over with my current Kickstarter project. I've known him for a few years now, and I believe in his project and that's why I backed those two.
The third successful campaign, I backed because the aforementioned owner of the first two projects told me about the campaign and I loved the project. I fell in love with the artwork. In addition to being a tea artist, I'm also a visual artist and I found her artwork to be compelling and unique and truly beautiful. That's why I backed that campaign.
I found that after launching my own campaign, that there are so many cool projects going on out there and I wanted to be a part of them. That's why I backed most of the campaigns that I have.
Others, I got to know the people that were launching the campaign, either because they backed me and we got to talking via message on Kickstarter or I discovered their campaign via twitter and got to chatting with them there.
My motivation to back most of those is because I saw a creative project and I wanted to help out a fellow kickstarter.
And for the projects that involve tea, I backed because ... well ... tea. I've got a hot and heavy thing for tea.
ETA: my campaign, just in case someone wants to go back me:
https://www.kickstarter.com/projects/497705217/the-great-52teas-take-over