I think the answer to that is fairly straightforward. Intel isn't in the business of producing RAM. They would have to buy and integrate a third-party product which is likely not something their business side has ever contemplated as a viable strategy.
If they can sell the board with more RAM for more than their extra RAM costs, or can sell more GPUs total but the RAM itself is priced essentially at cost, then it's not a cost center.
That's not what a cost center is. There is an opportunity for them to make more money by putting more RAM into their GPUs and exposing themselves to a different market. Whether they physically manufacture that RAM doesn't matter in the slightest.
