>>280353131 (OP)
The real answer is because if the series was too edgy it would put the company publishing it under pressure to regulate.
It's the same reason the ending for Attack on Titan is so bad. It was obviously forcefully changed to be more socially acceptable.
There are actual regulations like minor characters not being allowed to drink and nudity being restricted, but there are also soft regulations like not having your main characters kill defenseless enemies.
If they depicted these things, there would be outrage from parents unions to ban anime or atleast heavily regulate it.
Fullmetal Alchemist would be taken off the air, its manga not sold in stores, and the reputation of the publishing companies ruined.
It really has no meaningful in-universe explanation, it's purely external pressure
