i think that the band can afford professional security so that none of them incl. their staff are in danger. the major reason is that playing in those countries would make no sense from the business point of view. hardly anyone there can afford 55€ for a ticket so they'd have to lower the ticket prices dramatically, you'd have to pay for extra security, and no-one could afford buying gimmicks like t-shirts, tourbooks etc. so the reasons why they don't play there anymore are economical ones...