Migliacars is right. The whole situation is far too complex. Swapping bodyshells was not a problem in the past and the DVLA points-based system for keeping the registration is a recent thing, in the grand scheme of things.
You can't just accuse people of having a 'dodgy' car because it isn't how it left the factory. You certainly can't remove these cars from their rightful owners. Most aren't stolen, they are modified and messed about with over the years and as above, some people are so desperate they use an old registration on a newer vehicle to save £140 a year.
Don't get me wrong, I utterly hate seeing a 60s/ 70s logbook on an 80s car, but it is not possible to police this without massive manpower, or indeed prove the swap was done to avoid paying road tax. The DVLA do not know what to do about it, clearly. As I said above, all we can do as enthusiasts is to avoid such cars or simply take them as they are- vehicles of unknown provenance that are to be taken on, knowing full well they are someone's 'creation'.
Buyer beware.