YANG model - only see Cisco and Juniper, no Arista, Alcatel

Curious in Yang Git Hub , under vendor list, i only see Cisco and Juniper. If other network vendor like Arista, Alcatel are not there; does that mean their device does NOT support YANG model ?
if not, how do people use Netconf/restconf/gRPC to do automation with them ? (as all these protocols rely on YANG model)

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