Because it is illegal and the drug trade fuelled by such culture is far more serious and far reaching in it's effect and impact on society than the largely unimportant death of a flawed pop star.
By allowing the behaviour of such high profile people to go largely unpunished or un-investigated the Police are effectively condoning such behaviour and the criminal counter-culture which thrives on it.
Of course, if drugs were legal, they'd be easier to control, quantity would be easier to control, chances of becoming addicted as badly as she did would be hugely lowered.
If they were legal, there would be no crime associated with drugs, gang culture would have no financial incentive and gangs would almost dissappear, with no profit involved in selling drugs, there would be no reason for people to illegal sell higher quantities of drugs, when everyone would just get known quality, legal drugs for lower prices from say, designated chemists.
Drug culture is no different to culture up until 50 or so years ago, before then, drugs were legal worldwide, with a heck of a lot less crime involved in the trade.
Some people will choose a life of being whacked out of their gord, and maybe dying early, its their life and their choice to make, some people work like dogs, getting up at 6am, coming home at 10pm, and having a heart attack and dying at 45, no one stops them or even suggests they should be stopped.
She took drugs, she maybe did, or maybe didn't enjoy her life, it was all her choice, she died, so what. People die, big deal.
