We still have lots of stray thoughts, responses and observations, now they just happen on blog posts, on social media and in other non-peer-reviewed venues. The Internet has driven the cost of publishing to 0, and peer review is the only thing left that makes academic publishing qualitatively different. If anything, publishing your thoughts online is better than publishing a traditional paper in every single way except for peer review.
Well, publishing online also has a reach problem. The nice thing about journals is that they consolidate all the material on a subject. Arxiv does this for some fields (and I guess similar aggregators in other fields) but really it is nice to have the thoughts still be _curated_, like a magazine, without necessarily being to a citeable/publishable standard.
