Dr. Adrian Kavanagh:

Yes. I gather it is the same in the UK's case. It makes sense. The literature suggests there should be an ongoing interest in the home country's political affairs. An obvious way to show such interest may be through registering annually. If one stops registering, there might be a pair of suspensions. First, the home country needs to consider whether the process is too difficult.

The other suspicion is that people have lost interest at this point and maybe they do not want the right to vote.