People talk loosely about canonisation as "making someone a saint". That's not actually what it's about. It's about official recognition, and the rationale is, as Joe Offer said, about symbolizing something seen as significant rather than everything about the individuals themselves. Rather the same way Pope Francis turning up to the White House in that little Fiat. That wasn't about endorsing Fiat cars as such, it was about saying in cconcrete terms some things that needed to be said.

Most "saints" no one ever heard of outside a small circle, and they never got canonised. Like Joe's grandmother.

And the one's that did get canonised weren't perfect.