One of the adult learning principles states that learning is effective when adults understand the purpose for learning. Any knowledge gain should have immediate relevance to them and have quantifiable benefits. This would motivate them to put aside time for acquiring that knowledge.
For example, if you want your sales person to take up a refresher product training course, chances are he will put it on the back burner, until he is told how the training program is going to help him increase his sales. Perhaps the training program has updated content which will help him highlight useful product features, giving him a competitive edge in his sales pitch, or the training program has essential tips to handle difficult customer objections.
Therefore, instead of simply announcing and assigning training programs to your sales members, it helps to clearly list out the benefits they would get from the training program. Chances are, there will be more enrollments to the program. Do share your views on the same.