Rules, lack of rules, single, twin........not the major cause of these accidents in UK, USA, and other places by any means. Pilots making decisions and running out of safe flight options that are commensurate with their personal skill levels continue to be the main reason for 'accidents'.
I say 'accidents' as at least here in England, the police no longer use the term accident to describe vehicular crashes. They're now known as collisions......as there is always a cause, and often someone or something to blame.