Going back to the fire question, I think that the shield that protects the ship normally, which is tied to energy, is a thin layer shield, when this shield takes weapons fire, the shield itself catches on fire. Once the shield is completely depleted, the next unshielded collision causes so much damage that the ship breaks apart. Especially because these ships are made of such thin, lightweight materials to be able to attain the speeds they reach.

Now the shield item pickup on the track is an overpowered shield boosts that exists around the ship, it is much stronger. However, it is in a ready state when activated. Meaning that when it sense an impending collision with a weapon, wall, ship, etc. it goes up to full power to completely protect the ship. However when no collision is imminent, it is simply surrounding the ship in passive mode to avoid disrupting the flight physics.

The competition commitee for the FX league decided that making this a short term ability added to the excitement and mayhem of the league.

See, it makes complete sense