I don't have any experience in this area, but I imagine that fintech is a bit different than messaging. It's not the amount of data, but the nature of the data.
I'd imagine you can't use scaling tricks like eventual consistency or simple sharding here. Traders are going to be pissed if their most up to date information from the exchange is a second behind what they can see.
It's already at the point where they have a line in their FAQ for the GDAX API that tells people where to colocate from for the lowest latency.
And all of that data needs to be stored damn-near indefinitely, and securely. And integrated with traditional financial systems.
I'd love to see some information on what it actually takes, as i'm just guessing here, but seeing as there aren't any bitcoin exchanges that can seem to keep the servers running smoothly during spikes, i'm guessing it's not a trivial problem to solve.