Primarily the state of its Linux driver, and rock solid support in VyOS (derived from Debian stable). For a router, TLS offload isn't so much of a consideration

Primarily the state of its Linux driver, and rock solid support in VyOS (derived from Debian stable). For a router, TLS offload isn't so much of a consideration when the system isn't doing anything at layers 4-7 in the OSI model. If I had to make a perhaps overly broad generalization, I see more Chelsio and Mellanox NICs used in end point servers, and more Intel used in DIY whitebox network equipment.