In order for a Git hook to run, it needs to have permissions set to allow it to be executable. If a hook doesn’t seem to be running, check the permissions, and make sure it’s executable. If it isn’t you can make all hooks executable like this:
chmod ug+x .git/hooks/*
…or if you want to make a single hook (eg. post-receive) executable:
chmod ug+x .git/hooks/post-receive
(Thanks to this post)