I agree about the GE where people are less likely to vote, but referendum was a totally different matter.
It just frustrates me that people didn't vote in the referendum - like you, I can't control other people and couldn't force them to vote. But I'm of the mind that decades ago people literally fought for the right to vote and people aren't willing to use that right and prerogative to do so.
13 million people being able to vote, and not doing so, is a very large amount which could have influenced the result.