Why is it advisable to enter a next-hop IP address when creating a static route whose exit interface is an Ethernet network?

Adding the next-hop address eliminates the need for the router to do any lookups in the routing table before forwarding a packet.
In a multi-access network, the router cannot determine the next-hop MAC address for the Ethernet frame without a next-hop address.
Using a next-hop address in a static route provides a route with a lower metric.
In multi-access networks, using a next-hop address in a static route makes that route a candidate default route.