Target market for stacked PRs are ICs who don't have much decision making power and let's be real do not care too much about the look and feel of a "launch site" for the feature. It's also something few if anyone is making a purchasing decision over.

Target market for copilot includes people with actual purchasing power and also many new users where this is an actual make or break feature. So this is worth the investment into design while stacked PRs is questionable. I actually question why they bothered with anything more than a blog post at all for stacked PRs (looking at the post it doesn't seem like too too much more than a blog post though).