Looks like the biggest part is a 37MB vendor bundle, so I assume those are all the libraries they use. It's 6.5MB transferred, but compression only helps with the network part, something still parses and interprets that JS.
I'm guessing at that size (37MB!), the bottleneck becomes the initial parsing and interpretation of the JS for most clients, rather than the transferring part, which is kind of bananas when you think about it.