It isn't that there is any one specific element that is a barrier. It's the full process that is not encouraging a significant number of Canadian voters to vote, and as Dr. Veale has pointed out, the numbers speak for themselves.
Yes, as you say, it's that one form, but I have two dozen emails with Elections Canada from the last couple of years to pin down what my final address was. This is a big issue, because Elections Canada ties you to the constituency in which you last resided, but that is not a clear thing, surprisingly. Furthermore, after 20-some odd years outside of a country, that relation, for me or for any particular voter, becomes a little bit fuzzy.
It isn't one specific thing; it's the entire process of getting the kit into my mailbox in front of my street and then getting it back in a timely fashion, and then having faith in what Elections Canada does. It's solid, but I don't know; did my vote arrive? I get nothing back from Elections Canada. Again, it isn't any one thing, as you point out; it's the full process, and I think Dr. Veale's numbers really speak to that.