That's because they've flown/crawled off and died beforehand. I had a moth infestation in my previous house and it was monstrous. Now I do a periodic check of all my garments. In the summer months more frequently because the eggs hatch in a mere two days, whereas in the winter they can take months to appear. The worst thing is that the eggs are nothing more than a sliver of silk "glued" to the garment which you can see by shining a light on it. I check under collars, lapels, pocket flaps, facings and the under armscye where I found grubs on three occasions!
Take no chances, use old-style mothballs; they stink, but they work. Cedarwood is worthless. Luckily I live in a newer house now; fewer dusty nooks and crannies for them to live in.