The same reasons that have people going for M.2 NvME sticks instead of HDDs or SATA SSDs.
People often want data security on a dedicated machine and they access it from clients.
With 100GbE, one can have its precious data on a server with RAID or ZFS etc, which can tolerate failure of single drive (or more) and access it without network at full speed as if it was local.
I’m sure there are plenty of other uses, too, like AI etc.
For those that see that as an overkill, there is cheaper 25GbE model. Also, BIG difference SRT 10G stuff is RDMA+PFC+ECN.
RDMA means that data is copied directly to RAM for an application to use directly without CPU involvement. This means that even high traffic doesn’t interrupt the CPU.
PFC and ECN mean that data congestion is largely gone - neither switch nor target machines drop the data off the cable simply for being overwhelmed by the sender.
This is another BIG deal, for latency (no retransmissions), bandwidth and CPU usage.