That's a cool observation - it could just be GP's natural turn of phrase. I know a few people who never use any contractions when they speak. I assume it's a local/familial style.
I would not have observed this on my own. Do contractions make English harder to comprehend for non-natives? I'll have to avoid using y'all'dn't've
Yes they do
Common English. The "n't” contractions are the most comfortable, and "can't" is most comfortable because it saves a syllable.