Very interesting. Just to add a data point: I live in Germany, we also struggle with participation rates, even though out voting system is much easier. Here are the differences I can think of right now:
- Every eligible voter gets an invitation mailed to their home address, no registration required. (But a national ID, which virtually everyone has, because you need it a lot)
- voting by mail is free and does not require any excuse, how to get a ballot is written down on the back of the invitation.
- voting in booths always happens on a Saturday and is very efficient, I have yet to see a line longer than two people.
- No voting machines. Paper ballots and boxes only. Counted by hand, results delivered by courier.
- elections are spread over the time, it hardly ever happens that you vote for multiple levels at the same election. Which reduces the number of ballots per election.
- How many marks to make where and what they mean is written on the ballot. (the meaning explanation is often very short and only helping if you already know the general process)
- on the equivalent of your state and national elections, there is a website called wahlomat (election machine), which tells you about party positions and can measure your alignment with parties using a questionnaire. It is publicly financed and completely anonymous for the voter.
- If and only if candidates decide to send it, you receive their program in the mail. Which is pretty often for lower levels, but higher levels usually choose to rely on web pages.