Why do you keep referencing the number of sub-races? The only reason that halflings are in the top 9 is if you combine the sub-races. Split them out and suddenly halflings aren't even in the top 10 anymore.
I reference the number of sub-races to show you how many different options there are. There are around 100 canon racial options Of those, halflings are in the top 9. They are literally in the 90th percentile for races.
dragonborn and tieflings. Two races with nothing especially outstanding about them, no long history, no hugely famous authors to point to for inspiration, no movies - are both significantly more popular than halflings and a number of other PHB races.
I've answered this several times.
First, tieflings
do have a long history, in Planescape. I realize that they've been reduced to canonically being created only by Asmodeus, but nearly every person I've ever seen or heard commenting on tieflings prefers the original Planescape version--even those people who are too young to have every played in Planescape when it first came out seem to prefer the original tieflings. This isn't an in-game lore history, but it's a history of extreme coolness in the game. Tieflings, secondly,
also have the cool edginess factor to them. It's not at all surprising that they are popular.
And dragonborn are
literally dragon-born. Or at least, great-nth-grandchild of a dragon, and you could change their lore to say that sometimes the fetus in a dragon's egg forms into a couple of infant dragonborn instead of a single dragon wyrmling and not change anything in their lore. Regardless, being a dragon is cool, and until something better comes along, they are the next best thing to playing a dragon. Again, it's not at all surprising they're popular.
Halflings, the small, stoic, sneaky, everyman people of the world, are
also popular, even if they're not traditionally cool. Because their small, stoic, sneaky, everyman selves fill a purpose in D&D the way no other race really can. They're the anti-hipster people, and that's just fine.
Hang on. Since we're being all "honest" and all. There are several adventures in those 14 adventures, which have zero halflings. So, how are they performing the same function? And yes, they are just "there" and almost never serve any real function to the adventure. You could yoink every reference of halfling out of most of the adventures and nothing would change.
Keep moving! I can still see the goalposts!
You could also yoink every reference of an elf, dwarf, tiefling, dragonborn, or anything else out of the adventure and replace them with human and nothing would change.
Especially not now in 5e where you can give NPCs any traits you want instead of making them exactly like PCs.
You don't like halflings.
You don't think they're popular enough. That's fine. You can think whatever you like. Your opinion does not match reality or have anything to do with what WotC will put in the next edition.