This can happen for a few reasons:
* Seasonality: Many deciduous shrubs lose their leaves in autumn or winter as part of their natural cycle.
* Drought: Shrubs can become leafless if they are stressed by lack of water.
* Disease or pests: Certain diseases or insects can cause leaves to fall off.
* Pruning: Shrubs are often pruned, which can result in them being leafless for a period.
The term "leafless shrubbery" is often used to describe a landscape or garden that is bare during the winter months, or to highlight the structural form of a shrub without its leaves.