Why don’t people do the thing you have asked them? Assuming all other things are ok (such as it is ok you ask them to do something, and they know who you are ;)) it might not only be a lack of knowledge.
There are often three reasons why people do not pick up certain activities:
1. Knowledge
The apparent problem is that you can ask people to do something. They might say yes. Though if they lack the knowledge of what to do or how to do it, nothing will happen, or at least not what you expected.
Besides making sure there is knowledge, also spend enough time to make sure there is an understanding of it.
2. Discipline
Keeping up with a task requires knowledge. However, it also requires discipline. One needs to learn what to do and to be able to repeat this without constant outside motivation. You do the work whether you like it or not. That is discipline.
The trick to success is to choose the right habit and bring just enough discipline to establish it.
Gary Keller
3. Should it be me
People might have the knowledge and the discipline they need. However, it does not mean that they consider themselves as the person for the job. They might believe somebody else is better or cannot see themselves as the one who could or should do this.
This is where you might need to step in to help the person imagine why they are the right one and how they make a difference by doing this. Please don’t do the work for them, though be close enough they feel safe to do this.