I regularly interact with single-use period products. They are, along with other disposable period products, considered single-use because the majority of them are no longer effective after one use. Single-use period disks are an exception to this, because they are made of plastic and collect menstrual fluid rather than absorb it, and could probably be washed and reused a few times, although it is not suggested on the packaging. Pads and tampons absorb menstrual fluid and cannot be reused. Pads are made of absorbent material with a sticky plastic backing and are individually wrapped in plastic. Tampons are also made of absorbent material and most come with two-part applicators, typically made of plastic, although there are also cardboard ones, and are also wrapped in plastic. All of these are sold wrapped in plastic, in boxes, or in bags with multiple individually wrapped products.
Periods have been stigmatized for a long time, and that is reflected in period products. Things are individually wrapped for both sanitary reasons and ‘privacy’ reasons. The individual wrapping allows the used item to be wrapped before being thrown away.
Used pads and tampons are thrown in the trash and end up where the trash is taken. Although plastic applicators may be recyclable, it seems unlikely that they would actually be recycled for sanitary reasons.
