According to minecraft.net the only thing 1.12.1 did was fix two bug, "Make some opimizations" and do something with the credits, couldn't they just have waited on fixing that until they have something to add or maybe a little more to fix?
I guess there's no pleasing everyone here. See, if Mojang wouldn't have fixed this bug you can be sure that some players would have started commenting on how "Mojang doesn't care about the community" and now that Mojang has squashed the bug others like yourself suddenly think the update wasn't good enough. Now, I do agree with you that Mojang could have been more open about this bug, but instead they hid it so it's not quite clear what got fixed.
The bug they're talking about was an item duplication glitch in the recipe book. This made it extremely easy to duplicate items, even where things got ridiculous (getting a stack of 75 items which couldn't be stacked in the first place for example). Basically any item you dropped on the ground while you had the recipe book open was in risk of being duplicated.
So this was definitely not a pointless update. However, I do agree with you that they could have been a little more open about it. However... Fixing a hidden bug; since when are bugs hidden on the Mojang tracker? Shouldn't that fact alone be enough to realize that this was a big issue?