Curate, connect, and discover
I can't remember the specifics of when Izaya started getting access to the underground but I'm guessing it was pretty young for normal standards...actually given the common trend of gang warfare maybe not. But I feel like he got a little more deep into it than any of the colour gang leaders did. Like didn't he get recruited by Kine?
Anyway, given that and his apparent brilliantness its no wonder so little was done about his delinquency. Even his fights with Shizuo. Like imagine being a teacher for him, and trying to inforce the rules, only to have the knowledge that some yakuza guy has got this kids back for whatever reason. "Oil barrels? I don't see no oil barrels?"
On one hand, no wonder he comes off as a little bratty, but can you blame him? You try being a teenage guardian to two younger sisters. I can see why he might have signed up for an easy route too. I know his parents might have sent him money, but how much of that would really help him? He's a student, if something else came along that allowed him to afford a babysitter I wouldn't blame him for taking the deal.
And imagine growing up where some of the only adults in your life were criminals.
There are so many things that tie into how fucked up he is.