Part of the reason D&D archery differs from real world archery is proficiency.
In the real world, it takes years of training to be good military longbowmen. A crossbow, on the other other hand, could be taught in a few weeks. It's much easier to aim.
But in D&D, and RPGs in general, you're either proficient or you aren't. Your class gives it to you for free, or you spend a feat on it. Learn either one by adding the feat, takes a few seconds with the pencil and your character sheet and you're done.
Another difference is the timing. Battles in real life took place over a day, and archers of any flavor tended to be dug in or otherwise protected. Rate of fire was limited by how quickly your scavengers could collect spent enemy arrows and get them back to your archers. Nobody carried the hundreds of arrows, per man, needed for an all day assault. Instead you'd shoot your supply at the enemy as they shot theirs at you. If your troops were advancing you or designated scavengers would collect the arrows from both sides and get them back to you. If your side was forced to retreat you ran short, since you can only collect the ones that land within your own ranks.
Specifically though, your rate of fire wasn't limited so much by reload time as it was by arrow supply. The only time you needed to rapid fire was when an enemy force charged the archers' position and you lacked the infantry or fortifications to stop them.
In D&D, all battles that PCs are involved in are rapid-fire skirmishes, begun and finished in under two minutes. The ability to shoot faster is far more important in that setting, and arrow supply is often ignored.
In that setting, losing a full round to reload is a fatal weakness.
Some of the heavy crossbows of the middle ages had a small crank-action winch that drew the bowstring. A man of just about any strength could work one, but it was time consuming.
Medium crossbows often had a stirrup of sorts at the firing end, so the archer could put their foot in it and haul back the string with both hands. Faster than the crank, but still slower than the longbow.
The light crossbow was almost a pistol, in size and operation. Okay, maybe a sawed-off shotgun size. But it could be cocked with one hand and fired with the other. Good for rapid fire skirmishes, though it lacked the straight knock-down power of the heavier models.
The Chinese had a type of crossbow with a box to hold the bolts and a lever action to draw and nock them. Rapid fire, but less punch than even the light European crossbow.
On the whole the crossbow was harder to make: Moving parts, and bow limbs that had to be heavier, yet could still flex without cracking.
In the real world (and in the game, though it's seldom played) you could shoot a shortbow while mounted. Long bows, on the other hand, posed a problem for the horseman: You couldn't shift aim from one side of your mount to the other. The long limbs of the bow couldn't swing past the horse's neck easily.
The final difference between the real world and the game involves how armor works.
In the real world, a crossbow could punch plate armor at short and medium range. Longbows were less effective at this unless they had special armor piercing arrowheads. ("Odds! Bodkins! " pretty much meant, "Oh spit, they brought cop-killers")
But since D&D doesn't use armor to reduce damage, heavy or light weapon makes no difference. You hit the AC and you hit, period, whether it's with a javelin or a juice glass.
As a side note: Some tests were done with "poisoned arrows". Arrow heads were made with grooves to retain a liquid poison via capillary action, then fired.
The speed of passage through the air pretty much scattered the venom in flight. Unless you were firing point blank, it meant nothing.
Arrow heads could be specially prepared well in advance, but they had to have grooves and hollows for poison, and then they'd have to be covered in wax, to protect it. Nobody ever did the "Dip and shoot" thing we see people do in games.
The tribes in Africa and South America (and Southeast Asia for all I know) that traditionally poisoned their arrows were more stone age, and didn't use arrow heads at all. Their arrows had sharpened wooden tips that they'd bake dry near a fire, to harden them. Once dried they'd soak the wood in the poison, and it would be absorbed.
In game terms we'd call them sort of the opposite of "master worked". They'd have penalties to range and accuracy, and do less damage.
Now, why do longbows rule in game? Probably because of Robin Hood, movies like Spartacus and similar cinematic scenes that inspired the authors. It makes a better visual image for fantasy art.
