One aspect beyond keeping the discussion threads separately -- the betas don't always come out at the same time.
I pre-prepare the beta posts so that we can let people know when betas are available right away, and while the betas are almost always released together, it's not unheard of for one to come out and another to be delayed until another day.
That's not stopping me from doing a combo post that could be tweaked before we publish it, but it's one reason why we don't. It's always a work in progress. I'm mindful that some people don't love the way the beta posts are shared, so I do try to cut down on posts for the public betas and the less significant updates where appropriate.
I definitely could have comboed iOS 17.6 and its sister betas because these were not particularly interesting releases and there were no new features, so I do apologize for that one. I'll try to be more mindful with the smaller updates.
Double beta releases don't happen too often, luckily.