It may be that Archbishop John Holder of the West Indies is doing so on a false prospectus:
The Archbishop of the Province of the West Indies has announced that his Province has adopted the Anglican Communion Covenant. It is the third to do so officially, the others being the Anglican Church of Mexico and The Church of the Province of Myanmar.
Archbishop John Holder
“Our understanding is that it is not an exclusive document; it does not exclude, but rather it helps to lead people to reflect on their role as Anglicans, and identify their responsibilities as members of the Communion.
“There are no penalties involved if you do not follow the Covenant and that’s an Anglican approach. We try and keep away from penalties. It is not punitive. It invites the members of the Communion to follow a different way, to remember their responsibilities to other members of the wider community, to respect where others are in their journey.”Or - and I guess this is where South Africa is coming from - these are the terms on which the Province has assented: and any attempt to promulgate penalties will be ignored. Only that will be in the time of a new generation of Archbishops and who can tell what they will do, being given a power they do not currently possess.
Or, more cynically, this is the public line to convince people they have no reason not to sign. It is, after all, a fair statement of what the Covenant says - just so long as you ignore (a) the origins of the idea, (b) the publicly stated goal of excluding The Episcopal Church in the US and the Anglican Church of Canada, (c) previous drafts of the Covenant and (d) the institutional framework within which the Covenant will be implemented.
And given the role of the previous Archbishop of the West Indies in creating the Covenant it would have been most impolitic not to join in.