You are confusing NPC halflings with PC halflings. Sure,
most halflings (the NPCs) don't pursue such careers - but this can also be said of most NPC humans, dwarves, elves, etc .
But the PCs? They're a different breed.... You'd have to ask the players "Why is your 1/2ling a _____?"
6 of my own:
- Warlock (pact of the Chain, Fey Patron, familiar: pseudo-dragon) - as a child she befriended an ancient pseudo-dragon who began teaching her simple, non-harmful, magic. The P.Dragons goal was to train her & once she was old enough send her out adventuring to acquire loot for him. She jumped the gun by a few years. Nothing unwilling about this adventurer.

- Barbarian (Ancestral Guardian) - the warlocks older sister. Very much the reluctant adventurer. It was her own poor choices that set both her & her warlock sister on the adventuring path. She's a barbarian because she fights in a completely untrained manner (rage) & this was the class that best represented that.
- Fighter 1/Druid +(Circle of the Land) - Before becoming a Druid he was an ordinary hobbit working as a baker & doing his duty serving part time in the towns reserve militia. Until he came into contact with a bad batch of gnomish potions, got transformed into a dog, & at the end of the adventure failed the save vs the effect becoming permanent. So he set off to seek help from the regions Druids. He's now a dog who can wildshape back to his original 1/2ling form. The only way for him to spend more time in his original form is to advance as a druid so as to increase his wildshape duration. It's more of a career change than being an unwilling adventurer. In either form though he helped defend the region during the Tyranny of Dragons.
Ranger/Gunslinger (Pathfinder) - This guy is a big game hunter. He comes complete with an elephant gun, plenty of ammo, a 1/2ling assistant (via leadership feat) & is often found in the wilds of Varisia on Safari. His goal: bag a sphinx.
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Garth, poor Garth.... He's a 1980s redbox basic edition 1/2ling (translates as "fighter with smaller HD & lv cap".). His claim to fame? Well, he
doesn't have a negative modifier to his con..... And he's somehow still alive.
Other than that? Yeah, he's pretty special with negative mods on 5/6 ability scores.
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Uno - My very 1st D&D character. He started off as an '80s era Basic edition 1/2ling. So essentially a fighter - though his inspiration was Bilbo. But he's been remade as a rogue type in every edition save 4e, including via house rules in Basic.
Somewhere along the line he definitely turned evil. If memory serves he fell victim to the altar in the Caves of Chaos.
And sometime after that he became an assassin (1st as houserules in 1e) - because he's a sneaky & now evil git + nobody would
ever suspect the
halfling....
(because the chart in the book tells you that there are no 1/2ling assassins
)
They aren't there in worlds I build/run because I'm told they should be. They're there because as the DM
I like them.
And I'm the DM, so my whim is reality.
Now if I'm a player & the DM says "There's no 1/2lings in my game"? That's cool. I've got about a million other character ideas. I'm sure I can come up with something that fits.
1) You do know they aren't unique to the FR, right?
2) Or you could just
add another page to the PHB with your "better" thing. Then you're happy & everyone else is as well.