There have been no known .sh sales in the years. Even if there had been one, "share" only is a medium key word. It's still available in several TLDs. And, BTW, do you really think you can simply register a name that has never been registered before and then sell it? This doesn't work.
sh is the same combination as the beginning of share.
illustration:
SHARE.SH
Hence the brandability. For example, if you'd promoter share.tc, people would keep forgeting the second part of domain, while with sh it will get stuck.