The contrib directory is just that. A contribution of items submitted by us (Implementation) and others. You will see some of it is very outdated and not of much use except as perhaps an example to do womething else.
As a consequence, since that is our (Your Impplementers and mine) area to keep common scripts that can assist in our jobs that is why it is placed in the path so it can be used anywhere within the root.
If you notice there is also a path to a site scripts and bin directory which are not automatically included. This would be for site specific scripts or executables.
If you want to make the Tcl and Perl scripts generic on a Unix box just change the top line to: #!/usr/bin/env tcl or #!/usr/bin/env perl
FWIW, I copy my contrib directory to each new root as I have stuff in there I want to use with each one
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