Very interesting question!

And I don't think either that the linked Wikipedia article answers the question.

Unfortunately I do not know the answer for sure, but I might have some relevant information to add. So, from my studies I know that Barr-bodies are not totally inactive, they, in fact, do have some very limited transcriptional activity. It might be low in intensity, but still vital? I'm just guessing.

My other guess is linked to the development of a Barr-body in a cell with two active XX chromosomes early during fetal development. So this happens via a process called X-inactivation in which a gene called Xist becomes active on both X chromosomes, then another gene, the Tsix also becomes active on one of the chromosomes and suppresses Xist on the other (the process of selecting which chromosome becomes the Barr-body is random, hence female mosaicism). The one with the suppressed Xist remains active, the other becomes the Barr-body. So, the point is, that for correct X-inactivation, the interplay of two X chromosomes are needed, and people with Turner syndrome have only one. That might be the problem, e.g. the Xist becomes active on the one X they have and starts interfering with the normal functioning of the chromosome, and there's no Tsix to suppress it.

But, again, I'm just making educated guesses here.

Very interesting question!

And I don't think either that the linked Wikipedia article answers the question.

Unfortunately I do not know the answer for sure, but I might have some relevant information to add. So, from my studies I know that Barr-bodies are not totally inactive, they, in fact, do have some very limited transcriptional activity. It might be low in intensity, but still vital? I'm just guessing.

My other guess is linked to the development of a Barr-body in a cell with two active XX chromosomes early during fetal development. So this happens via a process called X-inactivation in which a gene called Xist becomes active on both X chromosomes, then another gene, the Tsix also becomes active on one of the chromosomes and suppresses Xist on the other. The one with the suppressed Xist remains active, the other becomes the Barr-body (the process of selecting which chromosome becomes the Barr-body is random, hence female mosaicism). So, the point is, that for correct X-inactivation, the interplay of two X chromosomes are needed, and people with Turner syndrome have only one. That might be the problem, e.g. the Xist becomes active on the one X they have and starts interfering with the normal functioning of the chromosome, and there's no Tsix to suppress it.

But, again, I'm just making educated guesses here.