It is an expensive venture to send members of a police force to another country, particularly if they are not available for full-time deployment. In addition, it is not always possible to have a surplus of staff like the military, particularly as there may not always be the need for manpower. It may be months or even years for this need to come across and in the meantime, to have the officers on hand would be a waste of resources such as time and money.
Some member countries have been forced to send officers who lack the expertise or experience to police other nation states but with a lack of suitably skilled employees, there appears to be no other alternative. Recruitment can be difficult when officers are deployed for terms of years rather than months, particularly if they have a family or some form of commitment in their home environment.
Assisting other nation states can cause disagreements about how society should be controlled and what laws enforced such as the United States attempting to make Iraq a democratic state. The western military have been training local armies and police officers to make a positive difference in the issues the nation states have faced but some have turned on their trainers, at times using deadly force. There is also the chance that authoritarian regimes may be assisted to repress their people, even if the intentions of the helping nation state are of a well-meaning nature.
On the other hand, there may be a complete reliance on the assistance but once the initiative has been completed and the police decide to wrap up their work, the nation state may return to the poor quality of life and issues experienced previously.
There are many difficulties faced in the nature of international policing, despite its well-meaning nature. Some of these issues can be overcome with time or organisation; others will continue to make the job a difficult task.