Remember that the Tempo would've also had quite a few fleet sales. Doesn't mean it's a great, or even a good car, it just means that Ford managed to undercut all other bids. The DS, on the other hand, would've had mostly private sales (maybe a handful to higher levels of the government, but that'd be about it).

Also, the Tempo was introduced in a more prosperous time than the DS, and has been said, sold to a much bigger market.