I am positive he is trolling us, but here we go;
With just a bit of more effort, you can make a reliable ranged weapon with retrievable ammo that can be discharged whenever you want by pressing a trigger.
Retrievable ammo? You do realize that this is not realistic, right? If the bolt pierces something enough to damage it it'll be damaged too, and unable to be used again. Also, a gun fits all the above requirement, is more commonplace, and just plain better.
Beats a throwing spear, a punching pneumatic thing or a car bumper any day in the week.
Spears are useful at close-range combat, and far easier to craft and use than crossbows. Power fists are pre-war, rooted in lore and serve an actual purpose; give you an edge in melee combat. Car bumpers are used by 8 foot tall, muscle-bound superhumans for the same purpose. Not the same as a weapon that is completely inferior to other, more common weapons at any range.
There are mechanisms so simple any poor schmuck can construct them. Most of them are basically things that hold the drawn bow string combined with the bolt groove and the bow itself.
True. But your mechanism will hardly be able to dent a tin can at ten meters, let alone kill a man at more than fifty.
And why would there be any wooden parts? Practically no modern crossbows has anything wooden on it.
Because everybody has advanced synthetic materials and production facilities to combine them in their backyards, hmm? Well, the Gun Runners have, but they wisely prefer to stick to their namesake.
And even if the potential crossbow in the game would have been made wooden, so what, half of the weapons in Fallout are wooden.
True enough, rather than chop down wood, you could use the stock of an existing rifle and build up on it, I suppose. As to why you would do all that hard work to build an inferior weapon, I don't know.