Milestones are often not met in project management for several reasons:

1. **Poor Planning**: Inadequate time estimation and unrealistic resource allocation can lead to unforeseen delays.
  
2. **Scope Creep**: Changes or additions to the project scope without proper adjustments to timelines can stretch the project beyond its planned milestones.

3. **Inadequate Risk Management**: Failure to identify, assess, and mitigate risks can lead to setbacks and obstacles that affect project timelines.

4. **Communication Issues**: Lack of clear communication among team members can lead to misunderstandings and delays in work completion.

5. **Resource Conflicts**: Dependence on shared resources or personnel across multiple projects can lead to conflicts that delay milestones.

6. **Insufficient Stakeholder Engagement**: If stakeholders are not adequately engaged, their feedback might come later in the process, resulting in rework or adjustments that push back timelines.

To improve milestone achievement, it's important to regularly review progress, adjust plans as necessary, and ensure that all team members are aligned with project goals.

Here are some follow-up questions to consider:

- What specific milestones are currently at risk of being missed in your project?
- How often do you review and adjust project plans to adapt to unforeseen challenges?
- What strategies are you employing to enhance communication within your project team?