Well there's a suprise. I have a theory - Because FIAT could have made little money selling RH drive Cromas in the UK, are they trying to make some back by ripping us off on the parts?
Heee heee ....
However I don't think people really understand manufacturing and parts supply.
EVERY part number costs any concern a large amount of money to:
(a) have that unique number
(b) store that part number (physical space, stock control)
(c) make that part externally available to customers (order & shipment)
(d) etc. etc.
Now I'm not defending Fiat but they and all other car manufacturers will have to make a cost judgement on what bits to stock and supply. Ten to twenty sub-parts or a complete assembly. In this wiper case they have chosen to split the product into two parts/nos. Motor on its own and motor plus linkages. Why they didn't list motor and linkages I don't know.
I remember in my early engineering career back in the 70's going on an "Understanding Manufacturing Course" held at a real manufacturing plant. Here we were politely told that the most cost effect and ideal solution for a manufacturer/supplier was to have but just one part number.
Example: P/N = 00000001 a simple stick on label/badge with the words FIAT
Now WHAT IS CRIMINAL in Fiats parts system is the number of parts that are annually dumped and removed from availabilty. In many cases the European 10 year rule after production is followed. If you are lucky your older than 10 year old car with have parts that are used in models much later than yours (pistons, rings, nuts, bolts, .........) If it is body trim then you can be in realy difficulty LONG before the 10 year time.
Less than a year after we bought our Strada Abarth in 1988 many body parts and trim were not available. Even the track control arms with wearable ball joints were no longer available from Fiat.
If you are lucky when Fiat clear parts out they will try to find an indepedant supplier that they 'cut price bulk sell' the parts to. Otherwise they will be just scrapped for scrap value.
Who said "A Car If For Life". Only make I know this is valid for is Ferarri where I gather for every production car ever made you can still get original Ferarri supplied parts. Very comforting if you can afford to buy and maintain a Prancing Horse in your stable of vehicles