Why is Prairie mustard seed sent to other countries for processing?

If you're dining in France and your food includes Moutarde de Meaux, it is highly likely the mustard seed came from Saskatchewan.

Why is Prairie mustard seed sent to other countries for processing?
A wde shot of an open field upon which yellow plants are growing.

If you're dining in France and your food includes Moutarde de Meaux, it is highly likely the mustard seed came from Saskatchewan.