It's because young people, for example, are highly mobile, and the address on the electoral register is not necessarily where they live. They don't necessarily listen to the radio, and there is something to be said for sending messages to voters that contain a policy or issue that they actually care about.
If I'm in Nova Scotia, I may not be entirely concerned with wheat and farming policies in Saskatchewan, because what affects me is fisheries or something else. Targeting doesn't necessarily have to be a bad thing. You can have targeting that is positive for democracy because you are speaking to voters about something they actually care about, and indeed in a medium they actually see and engage with.
We have a declining turnout, and this is not just a problem in Canada. It's a problem all over the place, and it's because the media landscape has completely changed. Part of the job of political parties in maintaining our democratic process is to adapt to that new environment and to develop ways of engaging voters in that new environment. Digital has to be part of that. If we do not have digital communications in an increasingly digitized society, we are going to dramatically affect the results of elections towards people who aren't online, which is a vastly shrinking population.
We shouldn't necessarily treat social media or online communication as a bad thing. Just in the same way that a knife can be a murder weapon or create a Michelin star meal, it's a tool. The appropriate thing is to look at what is reasonable for this tool, work out how to use it, and create boundaries for it.