Simple...magazine coverage of new amiga hardware, now getting the coverage aint so simple but if you build it and advertise it they will come. If a good article in a large computer/gaming magazine came out and lets say that magazine had just 100,000 readers (many computer/gaming magazines have many times that) and just 1% of the readers bought an amiga do the math! now times that by 10 articles in 10 magazines.
The other answer is obvious we are the ones who can keep it alive, we need to be welcoming and helpfull. If we get cult-like and closed society no one will want to be involved.
I know this is wishfull thinking but If ya dont dream it cant happen!