In sparring there is a referee or someone to control the fight so you have to abide by the rules set.
Out on the street anything can happen, when sparring you know your opponent isn't gonna pull a blade or get some of his mates to join in!
To get as close to the real thing you have to drill pre-emptive strikes and work on the pre-amble that happens before the physical fight is on!
These are just my views but also shared by some of the best self protection experts in the world!