Short Game Times + Expensive AP items = Ooooops
Okay, so you are doing well on an AP caster. You've picked up some mana sustain via Tear, Chalice, or Catalyst. You now have enough to buy a Large Rod -sweet! More damage, here we come! A few minutes pass...
Now its time to decide what to "upgrade". Well guess what, since games are so short, slot efficiency doesn't matter, and completing items is so damn expensive, your best buy is... Another NLR! And another, and another! Why spend three times the cost of an NLR when you could just have 3 times the AP? Since the game is decided by 20 minutes anyway, what you really need to do is blow people up, not have nominal extra utility.
This is a huge problem right now. High end AP items are literally never worth buying. The balance team really f-ed it up this time. Even if games are extended a bit, costs are quite prohibitive in terms of power gained vs gold spent.