Dragin, as you must be aware, the Huanghai Plutus/Dachaishen and its "body-mates" are copies of the first generation Chevrolet Colorado (Thai/US)/GMC Canyon/Isuzu I-Series.
What ramaz talks about are the older pickups copied from the N50 and N60 generation Toyota Hilux.
But yes, you are right in saying that these are supplied by a handful of body suppliers (there is a Kawei subsidiary, besides Foday) because, for manufacturers which are small players in the pickup segment, it does not make sense to invest in a press shop, dies, body shop, design/modeling/prototyping teams for a product that hardly sells on the merit of looks, and where utility and economy are the deciding factors for the purchaser (especially in an emerging economy where pickups are not usually bought for "lifestyle/personal use" purposes).
Even large CV makers, which have the means to invest in the above, or already have those facilities at their disposal, would not necessarily bother if pickups in their lineup are not large sales-drivers.
Think of this as being equivalent to the situation where a company/emerging country sets out to make cars or other vehicles by setting up SKD factories where fully assembled bodies are sourced from a principal automobile manufacturer. Instead of one supplier and one assembler in a linear relationship, in the case of these pickup makers, it is one supplier and many "assemblers".
At the other end of the spectrum, in the case of dominant pickup players (the likes of Foton, GWM, Dongfeng, JAC, JMC), we are seeing the emergence of new designs in recent years (GWM Wingle 6, JMC Vigor, Dongfeng New Rich for example).
In the SUV segment, this trend is changing, and common "body-shopped" models are slowly losing currency. Those which are present in the market are not major sellers. Think of all those Isuzu Grand Adventure, Honda CR-V, Kia Sorento, or Toyota LC Prado clones there used to be 5-10 years ago!
This "same body with different logo" culture is now prevalent predominantly in the LSEV sector, given the explosive growth of this market in recent times, but for opposite reasons, i.e., low-priced cars in high demand, very few independent innovators, lack of regulations, easier molding processes with plastics or fiberglass resulting in mass production of car bodies like commodities. Readers will find examples of this in the mini EV thread on this forum.
OK, so that was pretty long