The massive blast radius is to ensure the death of the predator's killer/captor. Meaning that even in the event that they managed to get to a vehicle & attempt an escape, the massive explosion from the self-destruct would more than likely kill them anyway.
Which brings into question how Dutch could have possibly survived at the end of the first movie, as I find it extremely hard to believe that simply diving into a ditch for cover would actually save someone from an atomic blast.
Probably just another one of those "magic movie moments".