Actually, it was a FAIL for LSWC-HP ammo, not jhp. It failed the FBI test because it did not expand. That doesn't necessarily mean it is inadequate on the street. But apparently the FBI wants both penetration and expansion, and they want it even when the bullet has to pass through clothing (which is pretty much all the time).
In real life, bullet performance is a game of chance. How far from the muzzle will the target be? What will be the angle of impact? Exactly where on the BG will the bullet land? What bone / cartilage / other structures will be hit? It's a crap shoot. Sometimes it will hit soft tissue and sometimes it will hit hard structures. A bullet optimized for penetrating hard structures would be expected to perform better when that scenario plays out. But when that bullet hits soft structures, it may pass right through leaving a slow bleed-out and leaving the BG capable of continuing to threaten your personal well-being. Which way will your encounter play out? You won't know until after the fact, if then. The FBI is looking for the best of both worlds - penetration and expansion - because they believe that improves the odds for the outcome they want. They are probably right