Why do idiots manually deregister vehicles

Agree totally, at least that still leaves an official paper trail if you do it that way, what you describe has certainly happened in the past because the purchaser knew damn well they couldn't be traced, especially a few years back when local councils were charging silly money to dump either complete cars or shells, and before scrap dealers were really interested in old cars and parts for export, and abandoned vehicles were more of a problem.

Thats largely done to stop backyard crooks buying writeoffs with live plates, tags and paperwork for the specific purpose of swapping them on to an identical stolen vehicle, damaged vehicle auctions used to be an excellent source of these. I don't think the insurance industry wants to be seen to be facilitating that somehow. The other reason is that it guarantees anything they sell that gets repaired will be put back through vin and compliance.

Sorry franc that actually isn't the main reason.
The main reason was that certain types of "hobby"repairers/sal-
esmen were buying the damaged cars.No real knowledge of how to propperly/safely repair the underlying damage to the car(or worse in fact knowing but not caring)
Theres a case a few years back in point where the finger was clearly pointed at the insurance company for allowing this car to remain registered when it had chasis damage.
By deregoing a vehicle basicly the insurer is covering their rear ends.
So the vehicle gets derego'd and must go through a reinspection process

Got a listing in my emails today for a 95% mint body 88 LN61 Surf with a recent sick motor.

Inside & outside is pretty much as MINT & original as you can get for it's apparently untouched age (apart from a recent reco head)& STILL has the factory graphics on the sides.
Paint is as close to mint as you can get/ upholstery as well

It started blowing smoke recently & doesn't have the time to fix it so he DE REGISTERED it & put it on Trade.

%% )*)(% (&&( %$@#$ ()& muppet