Why does he not use (a weaker version of) Scarecrow's fear gas? It seems like it could be useful in his war on crime.
Why does he not use Mr. Freeze's cryogenic chemicals and gadgets?
Why does he not use Poison Ivy's plants to create immunities for himself or plant-based weaponry for combat?
Why does he not use Firefly's jetpack?
Why does he not base his vehicles on the vehicles that Gearhead drives?
Etc. Etc. Etc.?
Also, why does he not use his Bat-summoning device from Batman: Year One more often?