It's put together like that to allow you to unfix it and drop it right into/onto the guitar/scratchplate as a direct replacement.
When you're building a complete replacement wiring loom, new pots, the whole shebang, for your guitar, sometimes it's handy to build it all on a stiff card or plastic template. That way you can work outside of the guitar cavity with a bit more room. With a Strat, that's no problem, but the way the pickups and switches are mounted in that link would make it really easy for a relative newbie to guitar wiring to just unfix the kit from its backing, drop it straight into the guitar and solder up the last couple of connections.
I can't seem to find the link I had for the particular supplier, but they supplied high quality direct replacement wiring harnesses for all different makes of guitar, all mounted on a backing so they only had to be dropped in and connected up. The images would have been a good example, but you get the picture. As I said, a relative newbie to wiring could just drop them in and complete the wiring in just a few minutes.