Bash 3.2 doesn't support globstar:
$ shopt -s globstar
bash: shopt: globstar: invalid shell option name
shopt -s globstar,
** is just a plain non-recursive glob.
The bash NEWS page says:
This is a terse description of the new features added to bash-4.0 since
the release of bash-3.2. As always, the manual page (doc/bash.1) is
the place to look for complete descriptions.
New Features in Bash
w. There is a new shell option:
globstar. When enabled, the
** specially -- it matches all directories (and files within
them, when appropriate) recursively.
You'll need to update your bash to at least 4.0 (probably install one from homebrew), or use