system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: Why are all modern chemical weapons nerve agents?

Why aren't there chemicals in use that have a different mechanism of action like preventing oxygen intake or causing burns? What makes nerve agents the best weapons?
gpt
Conventional chemical weapons were not that effective in battle:
* Early chemical weapons were inhaled; so everyone started wearing gas masks, which nullified their effectiveness.
* Non-nerve agents which affect the skin are generally pretty limited,  you can make someone's skin itch or burn, but probably not kill them.  These burning/itching agents were used in WWI in conjunction with lethal inhaled agents to try to get soldiers to take off their gas masks, when the inhaled gas would kill them.  
* Most conventional chemical weapons require a lot of poison to cause death.  That meant that it was a very expensive way to kill X element soldiers, when compared to bullets and shells.  It also meant that the area of effect of a chemical bomb was very small, if the poison were spread over a large area it would not be effective.  

Weaponized nerve agents generally can be absorbed through the skin, so gas masks don't protect the enemy at all.  They also tend to work at much lower concentrations than conventional chemical weapons, so a set amount of chemical weapon might work over a larger area.  There are much fewer nerve cells in your body than say, muscle cells, and each nerve cell is proportionally more important.  If you develop a poison which can target one kind of cell, killing nerve cells would be debilitating and/or lethal much quicker than killing muscle cells.  This is why most venom found in nature are nerve agents.