What do you mean by "doesn't support huge capacities"? You can always add more channels in parallel.

Yeah, if you tape out a new chip; but that's a pretty vacuous statement. The capacities of GDDR6 modules available do impose a meaningful constraint on the total RAM that any given GPU can be equipped with, and while Intel is still struggling to get any foothold in the GPU market at all, it would be a big risk for them to invest in bringing to market a chip with eg. 4x the memory controller to compute ratio typically used by GPUs just so they could claim to have the cheapest 128GB GPU.

At some point you run out of pins, and the routing gets harder and harder. GDDR6 has very hard constraints on signal path length/quality. It gets expensive very quickly.