Tomatillos are a tantalizing addition to any vegetable garden, when mother nature smiles upon us and all goes well bountiful harvests are not uncommon. Dissappointment however is a distinct possibility, at times when we peel open the outer husks to our tomatillos there is no fruit inside ... Damn !
There are a number of reasons this occurs, the most common being pollination, or lack thereof. Tomatillos are not sufficiently self pollinating, you will need at least two plants to produce ample fruit, preferably more. If you planted a single tomatillo plant it will probably not develop fruit, only an empty husk. If it does develop fruit, which has been known to occur with a single plant there will be less and of lower quality than you would have gotten with multiple plants.
The same will happen at times even if you do have multiple tomatillo plants growing but they fail to pollinate. The absence of insect pollinators, bees and butterflies will prevent pollination. Tomatillos are not wind pollinated they need the bees. If this is an issue in your area hand pollination is advisable, it's not all that difficult. See: Hand Pollination.
Environmental factors can also prevent fruit from developing. Although it is less common it does occur - extremes of temperature, a cold snap or excessively high heats. Excessive humidity and excessive moisture in a particularly rainy season can inhibit fruit formation in tomatillos. High temperatures or humidity causes pollen to adhere to the inside of the flower instead of the stamen, hampering pollination. When this is the case flowers frequently drop from the plant.
Although it is more rare some plant diseases can cause plant stress that will prevent fruit from forming.
If you harvest, or attempt to harvest your tomatillos too soon at times the fruit has not formed or fully formed within the husk. Be sure they are ready for harvest before plucking them from the plant.