When you are talking about criminal charges, then the burden of proof in criminal matters is "beyond reasonable doubt", and I can not see how you can possibly prove beyond reasonable doubt that someone inflicted an act upon themselves due to the behaviour of others. There are so many other factors in play.
Coroners and inquiries can still, and do, rule that bullying is a factor in an unnatural death, but the difference is a coroner doesn't have to prove this to criminal standards, and it's merely an expression of opinion.
If anything, I believe there is a shortcoming in terms of enforcing already existent law with regard to harassment, especially so in the online world and social media where people hide behind the anonymity of the internet to behave in ways, and say things that they could/would never get away with in a face-to-face scenario. Most people are capable of compartmentalisation and filing it away as "idiots on the internet", but not everyone can, it's bound to take a toll eventually when it's persistent and unrelenting, and the fact most people brush it off doesn't mean the bullying and harassment is a-ok in the first place.
I'm normally totally against internet censorship and government over-reach in terms of dictating to ISP's what they should permit private individuals to view and post on the internet, but with message boards and certain SM sites it's clearly gone beyond anything reasonable, and they permit their users to behave in all sorts of ways that wouldn't be tolerated in-person. There are historical examples of users or groups of users behaving in a manner that would constitute a breach of law had they being doing so in person, the problem is though, how do you convince a site based in the US (for example) to put a stop to the behaviour/and or surrender the personal details of a user who might have broken some law in the UK? It's impossible, and they'll simply tell you to get bent because they aren't subject to UK law. And no, irrespective of the harm they may be causing, I want no part at all of the UK becoming a place where the government dictates to ISP's that certain otherwise perfectly legal sites are to be blocked outright because a small number of users can't behave. That's straightforward censorship, and completely at odds with freedom of expression.