Milestones in project management can frequently be missed for several reasons:

1. **Unrealistic Planning**: Sometimes, the timeframes set for milestones are overly optimistic, not taking into account the complexities and dependencies of project tasks.
2. **Poor Communication**: Miscommunication among team members or between teams can lead to misunderstandings about project requirements or timelines.
3. **Scope Creep**: As projects progress, additional features or changes may be added, which can stretch resources thin and derail original timelines.