That is a question I have wondered about as well.
Here is what I could find with a simple google search . . .
Looking at the axiom that 85% of people come to Christ before their 18th birthday he says
People from an unchurched upbringing are a clear minority among evangelicals. (28% of people in church on a Sunday)
when someone from an unchurched background makes a lasting decision for Christ, it happens much later than we have often assumed and is spread out across every stage of life.
I must admit that the "85/18 Rule" was partially confirmed in my research. In fact 84.5 percent of evangelicals do accept Christ before that age. However, the statistic only holds true if they were raised in a home where both parents were Christians with either a high or moderate level of spiritual activity.
Taken together, these things suggest that faithful parents often bring their kids to the point of a decision (for or against) before they leave the parental home.
These kids of faithful parents will likely not be effective targets of "street preaching", as their parents have way more opportunities to train and reach them first. Street preaching may be effective for those from faith backgrounds who rebel against the family faith. (after they find life unsatisfying without faith)
I have been involved with mission and ministry on the rough edge (drug rehab, prison, food bank, soup kitchen) and in these places many people are dissatisfied with the way their life is now, and they may be more likely to listen to street preaching.
We have a guy who street preaches outside our Saturday Morning Farmers Market. People do not often stop and listen. I think he might be more effective if he had a relationship with his audience outside of just preaching at/to them. I can't speak to his calling as I don't know him. If God called him to this, then it is exactly where he should be, and what he should be doing.
I think street preaching works best with people already unsatisfied with their life.
This article quotes statistics from Thom Rainer, The Unchurched Next Door
A majority (66 percent) of Americans are unwilling to receive information through an e-mail message, and 70 percent say e-mail would be ineffective in getting them to visit.
I put street preaching in a similar category. You feel like a target, not a person or friend. Because you are already on your way somewhere else, street preaching does not target people who don't feel they have time to stop.