SORN - If Its Off Road Surely That's Enough?

Tonight I received constituent complaint about SORN.

SORN leaflet SAYS:
A SORN will automatically end if the vehicle is
taxed, or there is a change of keeper, before the
12 months are up.

A SORN is valid for up to 12 months and must then
be renewed if the vehicle is still kept off the road.

Constituent wants to know: why should he need to renew? Why can't they just assume it is still off the road, and if he later takes it on the road and gets caught by police for not having road tax, then fair enough. He feels it's a con that DVLA are working to raise money every year from people who don't realise they have to renew a SORN.