For Tor, DAC was cheaper and more accessible. By 2016, the prices for 10Gbase-T and SFP+ switches was often close to the same, but SFP+ gave significant flexibi

For Tor, DAC was cheaper and more accessible. By 2016, the prices for 10Gbase-T and SFP+ switches was often close to the same, but SFP+ gave significant flexibility while 10Gbase-T meant you had to architect specifically for it. With SFP+ hardware we had coax DAC for cheap connections, precut cheap fiber with hardwired transceivers, and of course expensive transceivers for longer range connections on fiber, and we could mix and match. A 10Gbase-T device meant we had to build the entire segment for new type of wiring, ensuring right NICs and switches, because mixing 10Gbase-T with SFP+ always required expensive transceivers (they were also not trivial to acquire in 2016, speaking from experience trying to unfuck a purchase of Nexus 3k in 10Gbase-T variant when all servers had SFP+)