MacOS – Yosemite three-finger lookup not working

Some older Macs only support two finger scrolling on the trackpad, not three. Since you're not seeing a setting for three finger drag, I'd guess your hardware just doesn't support it.

Are you able to do other gestures that require more than two fingers? If not, it's probably a hardware limitation, and you could just get a Magic Trackpad.

This may be one of those things that is labeled as a "feature not a bug." It's possible that the swiping gestures that are the same as the gestures on Snow Leopard are considered "Legacy" gestures. If that's the case then it is possible that having it "backwards" Is the expected behavior. If it's a legacy gesture then it may be considered to ignore natural scrolling because that is a "new" feature. I'm not saying that's how it should work, if you ask me if you change the direction of scrolling, it should apply to all gestures, not just the scrolling ones. I've moved mine back to the two finger option for the moment. You should file it at http://www.apple.com/feedback to make sure that Apple knows how confusing this is.