What causes the blockchain to be so slow, is it due to the fact that the internet speeds of these nodes aren't ridiculously fast like private trackers are? Or is it a totally different ball game?
It's a different ball game. The largest part of bootstrapping the blockchain, either on first boot or a catchup, involves verifying each block before proceeding to the next one. This is both a compuationally & disk access intensive process. There are ways that future clients could improve significantly on this, but right now the focus is on primary function & security, not performance.