If it's simple alignment like blast, they don't need the interconnect. But supercomputers provide all the other necessary needs: fast processors, connected nodes, accelerators, massive I/O bandwidth. Why build a cluster without a fast interconnect to complement those features? That's just turning down research customers. And 15% on top of the other hardware is nothing. The main costs is all the power, custom software, and support staff. And not all bioinformatics is ops on strings with minimal message passing.
For these guys, it's likely their best and only option. They probably weren't given the money to build a cluster optimized for their needs or to maintain a cloud instance. Why? Its oakridge, their main priority is HPC physics. It's hard to argue when you have access to such a HPC center. And HPC sites need all the customers they can get, lest their clusters get shoved into the cloud. It's a real fear. They'd end up with hidden costs, data lockin, and poor interconnects. To help pay for those peak massive simulations, traditional HPC need to fill up that last 10-15% and bioinformatics needs most of what they offer. Perhaps all that hard won knowledge will rub off on the burgeoning field too. :)
A vision of bio-oriented HPC is IU's clusters. Though they have a shiny new cray shasta with ampere and slingshot, several of their other clusters are 10 gigs with high mem nodes. All connected to the same storage too. The hospital is the main customer and dictates their designs.
Ditto on the paper though. It's what I disliked about Bioinformatics. All the glory to the researchers designing the experiments and they can't even bother to mention what software they used.