I've often been asked similar questions. New FS users probably don't realise this "design trend" can be explained by the development of the sim & not the 3rd party designers themselves. Let me try to explain.
The FS98 default aircraft featured a dynamic virtual cockpit (DVC) with functional gauges much like that used in FS2002. The DVC included interior views of parts of the aircraft visible from the cockpit. This feature was also included with CFS1. At the time it was not possible for 3rd party design programs to duplicate the DVC but most 3rd party aircraft included some sort of virtual cockpit with a static panel + the interior views & visible external parts of the aircraft.
FS2000 broke the mould & the defaults no longer had any sort of virtual cockpit. The new graphics engine made the DVC impractical so the idea was dropped in favour of extra views incorporated into the panels. The extra panel views, although made up of 2D images like the main panel view, give the illusion of a static 3D "virtual cockpit" with detailed side, rear & quarter internal views. These can include wings & those parts normally visible from the cockpit. The main drawback with this idea is that the panel is only suitable for one type of aircraft & further, one particular version of the aircraft as the paint scheme will most likely not match other liveries.
Most 3rd party designers went along with this trend, hence the FS2000 aircraft with no internal views. This was left to the panel designers. Aircraft with any sort of interior views will conflict with this type of panel, hence the lack of this feature in most FS2000 3rd party aircraft.
An extreme example can be demonstrated by aliasing the panel.cfg of a low wing aircraft with a DVC to one of these FS2000-style panels intended for a high wing design. You will end up with internal views which resemble some peculiar biplane. Consequently, very few aircraft designed specifically for FS2000 will have either a basic virtual cockpit or any internal views of the external structure.
When CFS2 was released, with the defaults featuring a much improved DVC, a few freeware developers got together with the M$ development team & Louis Sinclair (the FS Design Studio developer) to investigate the possibility of including the DVC in 3rd party aircraft. The results of several months of hard work are included in the CFS2 RAAF Expansion Pack by Joe Amodea & Jorge Alsina. The P-40 featured in the package was the very first 3rd party aircraft I ever saw with a fully functional DVC. FSDS was updated to include the new feature & Joe wrote a detailed tute explaining the process. This was featured on the M$ CFS2 site & posted on the Abacus site & in the SimV design section.
http://www.simviation.com/fsdesign_tute1.htmFrom this point onwards, most 3rd party aircraft designed specifically for CFS2 featured a fully functional DVC. Many also use the multi-LOD principle to improve frame rates which was another result of the research by the same developers.
Only now, with the "new" DVC feature in FS2002 are the FS designers starting to catch up with the CFS2 guys. If you want to see an example of the FS2000-style extra view panel, check out the default Lear45 which is basically the same as it was in FS2000.
PS. If you need a panel for that DC-3, try one designed for FS2000 as it will most likely include the extra interior views.