I'll take a stab at your question....
1. The popularity of a race choice in character creation has as much to do with the mechanics attributed to them as it does their lore. It's entirely possible a person might play a halfling because they want to reroll 1s and no other reasoning past that. Thus to some halflings are an enticing pick.
2. As has been said on every fracking page of this thread....there may not be enough lore for YOU to find halflings enticing but there is enough for others, myself included. In my campaign the halflings live in an area referred to as "The Greenway" and serve as a stopover spot for trade caravans and travellers crisscrossing between the human, elven, and dwarves controlled areas. They are known for their hospitality and exquisite baked goods.
3. Literally nobody on this entire thread has claimed halflings have "all this great information" that is "chock a block filled with flavor". Id be the first person to agree they aren't as popular in the history of DnD, however I believe that's true of every other race than the "Big Three". There is probably more lore and inclusion just for the gith in books and modules than there is for gnomes, halflings, half orcs, dragon born, and tieflings added together.
Do we give strikes against half orcs, half elves, and tieflings for not even being able to have lore at all because they are by definition individuals and not cultures?