The moniker "Affluenza Teen" already suggest someone with wealth. If this teen has the means to run, why would he not do so. His "affluenza" is a social ill which is perpetuated by people of means when they use their wealth and influence to duck consequences which would be unavoidable to someone of lesser means.
Yes, the police should have seen the "Affluena Teen" as a flight risk. This is a kid who was not only unable to make wise decisions, but who also refused to take responsibility for them. His psychologist said he was unable to distinguish right from wrong because he was so used to getting everything he wanted. Of coarse he was a flight risk.
When a person is affluent and has ample money and resources, they should always be considered a flight risk, no matter what the crime or who their family may be. The fact that he was simply ordered to probation was absurd in the first place, and now the government is to blame for his running off.
There is no way to predict how someone will react. Despite shows like Criminal Minds that suggest someone can be evaluated like a machine, people are not that easily defined and predicted. The human race is unpredictable that is what makes us so fantastic. If we were all robots, we would be boring. The proper and legal instruments were in place to ensure that the teen would comply with the orders. When he broke the law, the same legal means are being used to reel him back in. Unfortunately, he is on the run, which makes his situation worse for him and he will face those consequences.