He was talking about the nation, not the individual. When this commandment is disregarded, then the foundations of the nation are weakened. We know precisely why this is among the ten commandments. National survival depends upon gratitude. He who is ungrateful makes a poor citizen.
Poor citizens make a poor nation.
We see the fruits of it in family life. A lot of parents feel unappreciated. If you wonder about the frustrations that sometimes seem to grip them, that may be the reason. If you wonder why they sometimes lash out unexpectedly, that may be the reason. If you wonder why their punishment seems unjust or their attitude unfair, that may be the reason.