As often in those novels the author doesn't know anything about probabilities.
2% stays a small probability, even with 1000 hits, if you are unluky, the effect may not be triggered.
At that time, the effect of the instant death probability would be very obvious, especially for those Crown-ranked troops that were Meat Shield soldiers.
Tribe: I Become Invincible With My 10,000x Bonus From The Start