The reasons are simple:
It is a very simplified version of my more complex sheet
I never intended to build one, but eventually it built itself out of need
I do not want to appear competing with other sheets that I never tried anyway because I did not want to be influenced by anything. I do not know whether other models are good or bad as I have not tried a single one of them, too busy coming up with my own one :)
I did it all on my own so I get full blame or full glory, but I do not have the need to make it a public display either way.
Then again if one of you wants to make it freely available be my guest.
In other words it is a tool to use among friends and post here whatever results you get, or comments you have.