ZX Auto was never part of GAC; they had a strategic manufacturing partnership and a technology (R&D) joint venture.
The partnership was dissolved in 2017 following the Runpard fiasco and poor sales performance of the joint SUVs (Urban Ark derivatives). The R&D JV was wholly taken over by ZX Auto and the Yichang plant was taken over by GAC.
Please refer to posts 19 and 20 of the Terralord thread
As for BAIC, it does represent ZX Auto in a few countries in the Middle East/Africa region. Perhaps in these markets, ZX Auto has better reputation or brand recognition with regard to pickup trucks (from all the war video footage!), however the market may not be that large or lucrative enough that ZX feels the need to invest its own resources (more likely when BAIC or its local partner has already done so).