When this first came out I checked on my Pixel 7 which is on A14 already and I didn't have the apps available either.
They are now available.
So yeah, it's almost certainly on the app developers who didn't target the new API version available, not Google. New Pixels launch with new versions of Android, but you can validate the same issue on older Pixels who have already upgraded to the new Android version.
Google Messages (RCS app) does that. It even works from iMessage to Android but that is just because Google parses the SMS text that says they reacted that iMessage passive-aggressively sends and makes it appear correctly. It's not following RCS protocol, it's basic text parsing is all.
Incidentally, Google also started sending the same pass-aggressive reacted SMS messages to iPhone users for those using those RCS features, so now Apple gets the messages Android users had to deal with for years (and still do, if they aren't using Messages). I don't know is Apple is doing the same parsing or not as Google, if they aren't then somewhat ironically to Apple's intention Android now has the better react experience.
This whole thing isn't on Google. The app developers didn't update their target API so they were not available. My Pixel 7 is on Android 14 as well and they weren't available either until it just got fixed.