Think about it from Bitmain's (or any big miner manufacturer's) perspective: you're a money printing business in essence. You mine BTC in all the most profitable ways possible; mining with customer equipment for 2 weeks before shipping, charging hundreds of percent markup prices for mining units, adding proprietary boosting tech not activated on customer equipment etc. But you still find yourself stuck with thousands upon thousands of last generation miners that are now unprofitable despite all the advantages you ensured yourself.
So, you create an altcoin with the same hashing algorithm, and as compelling a marketing story as you can fashion. If you can get enough market momentum, your old unproductive ASICs can eek out just that little bit more profit before they croak. Maintain that narrative as long as possible, and you've added extra profitability from what would have otherwise been wasted capital.
Great point.
That raises another question; couldn't BCash also directly be initiated to prevent a worse case scenario where Bitcoin would fork off (yes, I know it will badly hurt Bitcoin) and deem all Bitmains equipment worthless? It's like a worst case scenario insurance for Bitmain. Without BCash, there wouldn't be anything to fall back on and people and professionals owning Bitmain gear would end up having hardware with little to no resale value because there is no real use for them.
It definitely puts things into a different perspective with this in mind.