Why was the SpaceX abort test not initiated by real booster failure?

Today (2020-01-19) SpaceX had a successful flight abort test. As far as I can understand, at a specific altitude, Crew Dragon fired its engines and escaped from the rocket.

This test looks like a very safe abort test, Dragon commanded Falcon to shutdown, and only then fired the Super Draco engines; if the booster engines were still firing, would it collide with Dragon? (i.e. the acceleration of the booster without dragon would be more than the acceleration of the Dragon by its Super Draco engines?)

My question is why did this test not use actual failures to trigger that abort? Like the booster stage explodes, and it is detected by Crew Dragon and triggers the escape system. That will be able to validate actual failure detection too.