See also cheap bulk spices at Indian markets. They are a goldmine for stuff that can be costly elsewhere, even if you are not interested in Indian cuisine.
My theory is that, in addition to having the right connections for cheap import, their customer base probably demands a certain price point for bulk spices.
Spices are cheap in those markets only because people are used to the completely nonsensical markups you see in grocery stores. Those little jars of mustard seed that cost $12? That's almost entirely markup. McCormick is a total racket.
For stuff like potatoes or beans it's really hard for me to care enough that I'm paying an extra $0.50 compared to the market down the street. Vegetables are cheap, unless someone slapped that organic sticker on it. It's just not worth the effort. But for spices I'll make the trip.
My theory is that, in addition to having the right connections for cheap import, their customer base probably demands a certain price point for bulk spices.