I said no human can achieve full enlightenment, not that it is not a goal line that is ever crossed. "If you choose to go back to Earth, it would be for the specific requirement to have the goal of growing your soul to get to the next level, only you are not consciously aware of it once you incarnate.
Once you enter and complete a few lifetimes you will start to feel comfortable knowing where you want to ascend and with whom. That is where your community of spirits come into play. We always come in with the same people/souls, lifetime after lifetime. There are about 80 to 120 of you together at any given lifetime. It is around this time where you the soul and collectively the community of spirits start to decide what level you want to attain and what price it will cost you on earth. [No pain, no gain]. Now you can understand that not everyone wants to attain nirvana as you say.
To attain nirvana, you would go on a completely different cycle, and that usually happens after a vast number of lifetimes lived. The lifetimes that you start to choose to live [at that point] are with great suffering. Think of the severely retarded, the severely mentally ill, POWs, people who have died violently at the hands of great evil and even still-born who give up their life experience for the host.
These life cycles will continue again and again and if you have lived your life according to our plan, will allow you to go to higher and higher levels. One obtains full enlightenment when there is nothing more for you to suffer, when there is nothing more for you to learn!"
I repeat, WHEN THERE IS NOTHING MORE FOR YOU TO LEARN.
That quote is not mine but it appears in several of my articles, in which I quote the words to spoken to me by my highest power. https://medium.com/illumination/i-speak-to-god-and-god-speaks-to-me-23bff8ec2274