Some ideas:

• Legacy reasons. Some projects previously used Consul and don't have time to migrate to the Kubernetes way.
• Consul is also K/V store. While, K8s supports configuration, currently changing configuration requires a restart of all applications. Watching Consul K/Vs for dynamic configuration might be easier.
• Consul supports the following which Kubernetes strictly doesn’t (but can be worked around):
• distributed locks.
• semaphores.
• leader election.
• Consul has a powerful concept of sessions, which connected to a healthcheck is pretty powerful.
• Consul supports proximity queries. Kubernetes does not. This is useful for low latency applications.
• There's some useful tooling around Consul. Including Vault integration.
• Consul supports fine-grained ACL. K8s has a somewhat less fine grained ACL, but I think there are extensions.