From what I've tried learn about, the problem is NOT only the cyber-bulling...
It is the whole society that is sick, for several reasons (most of these, do not matter now).
But thinking short-term and about a single individual, usually the reason why a individual keeps going online and attracting bullies, is that other stuff is broken on his life, for example that individual might be extremely lonely, giving rise to "attention whoring" behaviour (that quickly attract bullies).
I once made friendship with a girl that was a unhealthy amount of time online, even weirder, she started to treat me like the responsible person for her, even with we living 1500 miles apart... Over time I discovered her father was a dead-beat sort of guy, and her mother was extremely tyrannical, yet kinda lazy, refusing to take her to the doctor for example when she discovered she had yeast infection.
More digging on her life, trying to understand some of her bizarre behaviour, and I found out that her extended family abused her when she was around 4 to 8 years old, including people that were cops and supposed to be moral compass, the environment already her was entirely toxic, she for example regularly participated in lucrative (for her) pyramid schemes and believed them to be legitimate and normal, when I explained what it was, she was confused, and did not wanted to believe the community she was living was dishonest, later more question asked, I figured that she really lived in a kind of cesspool of dishonesty and backstabbing, with everyone being more or less friendly on the front, but always ready to backstab in name of survival, the place was poor, people used stolen electricity, internet was ran by a illegal ISP, her father ran a unlicensed bar on the lowest floor of her home, and bar brawls inside were common...
It became clear to me, that what drove her to attract bullies on internet, was desperation, she was stuck physically in a hard to leave place (a bus to the city downtown was 30 minute walk away, and then it was a 2 hour trip in difficulty terrain, also her parents forbid her from taking a bus anyway, she never used a bus and was already a adult), the only confort she had, was that sometimes random strangers on internet cared for her (like me), but obviously, seeking random hero strangers on internet, is also a very fast way to find random villain strangers (some that even might look like heroes on first glimpse).