Here’s the response I got from hubspot tech support.
This was an internal decision made by our Product Team to maintain consistency in the source code editor across the product, since the text does not wrap in the Design Manager. However, I have noticed several customers asking to revert back to the previous version, and so I’ve reached out to our developers to voice this.
I would also recommend commenting and/or upvoting about this same issue. The more traction a post gets the better, as it will get more visibility to the Product Team.
Hope this helps clarify things, and let me know if you have any further questions.