Cheaper to get, bulks it out, flavours it more efficiently? Any number of reason.
There was that apple sauce scandal in the US recently where kids were getting chunky doses of lead because waaaaaaaay down the production chain, some dude grinding cinnamon in Ecuador chose to bulk out his milling output with lead chromate (for the red-orange colour pop) amongst other powders which were not cinnamon.
More government testing up and down the production chain could help stop that sort of thing. Hopefully dodgy imports avoiding the tests at one level, would get clamped at another.