What sort of things did they point to? I'm not really familiar with their early arguments.
It is a complicated matter but, roughly put, the African churches pointed to the fact that, in the Anglican Communion, they were supposed to be equals with the English, Americans, and other "advanced" nations, but it never worked out that way. Instead, the English and North Americans violated both the rules of the Anglican Communion and the traditional Christian faith...and got away with it, while being simultaneously outraged that the African jurisdictions were contending for historic Christian (and Anglican) beliefs that had been targeted by the other group for revision.
And then, to make matters worse, this patronizing attitude was exhibited by the Northern churches by them telling the Africans that it was TEC money which was keeping the African churches going. This was going on, remember, while some of the African nations and churches are literally fighting for their existence against Muslim violence.
Then, failing to browbeat the African churches into submission, the North American and English jurisdictions decided to undercut their adversaries by bribing the minority of African churches which had not joined GAFCON in this never-ending struggle for supremacy within the fast-sinking Anglican Communion.
And by the way, if an onlooker were to think that the churches which are growing and/or count the largest memberships should be the natural leaders in Anglican affairs...
The Church of Nigeria is by far the largest Anglican church in the world, and is growing, and while the Church of England and The Episcopal Church in the USA (TEC) are losing members at a dramatic rate and the Anglican Church of Canada is expected to cease to exist altogether in a generation or so, so severe have that body's losses been in recent years.