Clownfish can sometimes be reluctant to spawn in an active, crowded tank. In my experience, being housed with other territorial species and/or not having an anemone can also be factors.
If you are really interested in them spawning, you can try thinning out the inhabitants of your current tank or putting them in a 20 gallon tank by themselves.
Conditioning them with live food is also an almost universal trigger for aquarium fish. I feed mine plenty of live foods and my Occelaris clown pair spawns every other week like clockwork. I’ve had the female for about two years and the male for one.