Not in particular to ipv6, it's THE future. but ipv6 itself is not widely used, so for that alone is an easy target.
Another point is, ipv6 has a large pool and it's pretty cheap, like dirt cheap. So unless the provider is honest and transpararent, you will most likely get allocated to the same subnet, hence why you see banwave happening.
According to this http://stackoverflow.com/questions/15265893/what-does-it-mean-64-in-ipv6
This means that when your ISP gives you a /64 they are giving you 264 addresses (that is 18,446,744,073,709,551,616 addresses)
You can rent a vps any time of the day, and they will give you /64 for free.
One other point https://slash64.net/
There's also one other thread concerning FB, and FB particularly dislikes ipv6.