Is there any evidence that the git commits weren't in the ROMs from months ago? The monthly ASB corresponds to when the bugs are publicly disclosed, not when they made it into ROMs.
The only way to get the full set of security preview patches is through GrapheneOS. It's strange Google doesn't ship more for the Pixel OS but that's the way it is right now. It takes them around 4 weeks to make a release and even longer when including the time for adding changes to it so there's a long delay built into the process. They should fix it but are clearly not prioritizing it without media pressure that's not happening. They do a lot better than other OEMs but that's much different from doing a good job.