At least when I looked into it last, it was less about price and more about availability. NIC's are easy to get, but the switches were a 50+ week lead time. I'm sure it has come down now though at least for my business, we are just focused on ethernet now. We can do 128 NIC's @ 400G into a single Dell Z9864F using ethernet. Few will need proprietary solutions for this as there are lower hanging fruit.