I was searching about induced pluripotent stem cells. I read this article https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6112416/ 

And it says: "While mouse cells are typically grown in a state of naïve pluripotency, equivalent to the naïve epiblast of the preimplantation blastocyst, human cells are cultured in primed pluripotency conditions. These are more similar to the postimplantation epiblast where cells become primed for differentiation."

So, hPSCs are obtained from postimplantation epiblast cells? Why don't they obtain it from preimplantation? Because preimplantation embryonic stem cells are naive pluripotent stem cells and they can differentiate into all of the germ layers. So isn't it an important reason to obtain preimplantation embryonic stem cells? 

Spoiler

 

 

That is not what I read; this article discusses cells which have been MADE to become pluripotent.

So mouse cells are, typically, grown in a state that is similar to what you would find if you examined preimplantation blastocysts. While the human cells are typically cultured in conditions which lead them to be similar to postimplantation epiblasts. 
This doesn't mean they are obtained from any of these cells, just that they resemble them.

While I am unsure if postimplantation epiblasts cannot become all germ layers as you suggest (could you provide a link or quote/citation?), just 4 lines down the article discusses: "

There have been several attempts to generate human naïve pluripotent stem cells (nPSCs) over recent years. Most often when putative human naïve cells are generated in vitro they are analysed using criteria that are known to distinguish mouse naïve cells from primed cells. Such criteria include responses to extrinsic and intrinsic signalling pathways, the biophysical, biochemical and metabolic status of the cells, and the overall epigenetic and transcriptomic cell identity. However, recent advances in our understanding of the human embryo also allow direct comparisons to the naïve compartment in vivo. Recently, cells exhibiting human naïve epiblast molecular features have been described [3••,4••,5••]. Over the course of this review we shall examine how closely these match the state of both mouse naïve ESCs and what is known of the human blastocyst.

". So yes it seems to be important, but did you A not read the article or B do you mean something else?

 

-Dagl