No one likes to spend his time in the office yawning and dreaming about sleeping during work time, that is just not professionalism. On the other hand I also wonder, if no one wants it than why they go through it? According to my very own experience, this habit “develops” from few factors of which the most important is not doing the work which you were chosen to do or not having enough of it. If you are doing something where you are good at, then this negativity wont happen.
Also lack of appreciation is a major cause, you can at least let the people know they have done a good job or don’t make them feel bad about their effort, so that they should strive for more and more. This type of demotivation leads to people not paying full attention to their work.
“Keep them interested” is a basic marketing term so that your audience pays attention to you and to organization, its employees is somewhat like their clients, so they should follow this mantra as well so it is better to keep them busy with the work which would benefit the organization in the long run and also those employees should feel that they are part of the organization as well.