Chromite (40%) might be priced around $400/metric ton right now (I'm not positive of the exact number, it's not quoted regularly on any sites that I know of).

Nickel is around $8.50 per pound, or almost $20,000/metric ton.

It all comes down to economics. Based on the lower value of chromite, you'd have to ship fifty times the volume to get the same dollar value.

Slurry pipelines don't make economic sense. The best way to ship low-grade ore is in bulk, without mixing it into a slurry that has to be treated again at the other end.