What should you do when key stakeholders don't attend your meeting

When the key stakeholders didn't attend the meeting due to the time, you should address the following:
1. Meeting time schedule;
You have to inform the key stakeholders at lest a week prior to the meeting, in order for them to plan a head for the scheduled meeting and set their priorities.
2. The importance of the stakeholders to attend the planed meeting (Prioritization);
Meeting agenda should be made clear and the importance of the meeting attendees since it's related with decision making and project constraints.
3. Root cause of unavailability of key stakeholders, if it's frequently.
Time isn't an excuse since the meetings is one of the tools and techniques to address and resolve the issues (Review, Change request, Constraints, etc.) during project lifecycle.
I believe if you communicate effectively the importance of the meeting to all project team, definitely they will priorities there activities and adjust their time. Other wise you have to amend the organization reviewing procedure to enhance with your project requirements.
Best Regards,