He finds it unreliable and difficult to produce on demand. This is not to eliminate love. Love is still a bonus. But respect becomes the foundation. And deBono goes on to enumerate reasons to chose respect over love.
Respect is durable.
It acknowledges another's dignity, while love puts demands on it. Love can be a hunger, a need, a temporary madness, whereas respect is understanding and appreciation. There is much more to this deBono treatise on happiness. Most of it is common sense. The required elements are humor, dignity and respect.