People seem to forget that Feyre's bonus chapter was initially part of ACOSF, but SJM and her editors pulled it out because it added nothing (SJM’s words) – hence why it became a bonus content for the special editions.
So when people speculate Azriel's bonus over Feyre's, it's not because "Gwyn wasn't included in Feyre's" – it's because there's nothing to speculate with Feyre's.
Apart from the info we gained on Feysand (Feyre wondering why Rhys had been in a mood lately, Rhys's reaction to the pregnancy, and the two of them coming up with baby names) nothing new was disclosed.
The tidbit on Elain was not a new revelation. Not really. We already know there’s more to Elain than meets the eyes. We already know she still has some lingering trauma so exactly what new information or crumb apart from that did SJM leave us to speculate further?
Because the bonus wasn't about Elain nor did it hint at anything substantial about her. How people managed to make Feyre's AND Azriel's bonus about Elain is wild considering she was not even so much as an afterthought soon after she left the page/conversation. If anything, Feyre's chapter in relation to her sisters revealed how strained their relationship still was.
Back to my point though, post and prior to the release of ACOSF SJM mentioned in her interviews that she wanted to revisit and enjoy Feysand again. Considering ACOSF was the first book from Nessian's perspective, it made sense why she wanted to write a scene from Feyre's POV regarding the pregnancy (bc that was the premise of her chapter) and why her editors pulled it out.
Thus, when people speculate Azriel's bonus over Feyre's, no, it's not because Gwyn wasn't included in Feyre's. It's because there's actually something worth speculating with Azriel's.
It's why SJM asked her friend to read his chapter.
It's why she said she scattered crumbs all over it.
***Also, it's worth reminding that B&N holds exclusive rights to Feyre's bonus. Just like BAM holds exclusive rights to Azriel's. Therefore B&N including Feyre's chapter in the paperback of ACOSF (just like how it was included in the hardcover) is not a surprise or at all unusual given they have exclusive rights to it.