Why does a struggling peasant-turned-bandit with only lowly leather armour have a long sword that he could not realistically afford?
Watch these videos about cheap weapons for the poor and inexperienced in the medieval ages:
Think about it, swords are much harder to make than an Axe, Hammer or Spear yet how many Poor enemies do you see with a Long sword, Bastard sword and even Short Swords? Practically all desperate bandits that have so little training that they die with a maximum of two arrow hits yet they all carry expensive, metal extensive, labour and craftsmanship intensive Long Swords. I have been playing a Badass of a game called Mount and Blade: Warband and all of the poor down-on-their-luck combatants strictly do not have expensive 'anything' let alone a 'noble's weapon': the Long Sword. One sees re-purposed farming and hunting tools and makeshift armours for these lowly untrained malnourished combatants. This makes sense in a real worldly setting that in most cases these impoverished people cannot afford a proper meal let alone a luxurious Long Sword only affordable for the rich and influential.
I get it, in Baldur's Gate swords are cheap and [wait a second on that thought].. Stop typing and fire up Baldur's Gate and go to an Inn. What does the "8 Gold" "Royal" accommodation say within its description text?
-"A truly luxurious experience, at an equally exorbitant price. Beds filled with the softest down, draped with the finest Calimshan silks and linens. Nearly as restful as a week in a lesser room, though who but royalty could afford the cost."
So if only "Royalty" can afford an 8 Gold Lions room according to our Setting's economy, than how can masses of peasants-turned-bandit possibly afford a luxurious Long Sword with a incredulous price of 22 Gold Lions (with an average reputation)?
I hear you say "they stole them" quietly in your corner. Okay who from? Commoners don't have Long Swords nor do even the odd ruffian. Than who has these swords? Blacksmiths, Soldiers and Caravan Guards and Beings that could easily kill a poor malnourished peasant-bandit with ~8 Hit Points.
Okay so where do they get the Long Swords? "The Iron throne!"
-They are rife with the Iron Plague of the Sword Coast.. Their Employers would not cripple their own forces.
"They stole them from Graveyards and Buildings!"
-Then why is their not one reference of this nor a case of disgruntled towns people offering a single quest to adventurers to rid of these unhonourable thieves stealing all of their expensive weapons en mass?
"Near the end of Medieval Europe (Which 90% of AD&D is based on and deep in ancient lore Faerûn was once connected to earth) Plate armour and Swords were not uncommon for lowly foot soldiers to have so maybe bandits could have Longswords?"
-Plate Mail Armour in Medival Faerûn Costs 900 Gold Lions, no lowly soldier in this setting can afford Platemail Armour that costs 900 Gold Lions and with that said I am very surprised to see the low price and high amount of swords that are used by all ranks of guards and soldiers in Baldur's Gate when historically in Medieval Europe Axes, Polearms and or Blunt Weapons would be more cost effective for their ruling powers to equip them with; and thus 'nine times out of ten' the ruling parties bought just that for their standing forces: Axes, Polearms and or Blunt Weapons (secondary weapons such as daggers were mostly financed by the soldiers themselves). Look at what most of the Scottish and English troops were issued with respectively in The Battle of Flodden
http://www.flodden.net/pages/tour/armed-for-the-fight . An interesting point is that when close melee happened, the over whelming majority of Scotts suffered direly from having no significant close quarters standard issue weapon and were thus massacred after their situational pike formations fell apart.
Lets face it, it was a bad judgement call from the developer who added Long Swords on the menu for the lowly peasant tuned bandit.
*Bam, Point Rekt -Interception was Successful*