Because the purpose is to craft, build, fight mobs. It isn't an RPG and they called it a Sandbox game
mobs
Passive mobs need light to spawn, and they only spawn on grass. If the aggressive mobs are spawning, then it must be night and the passive mobs will only spawn near torches, pumpkins, glowstone, etc. However, Notch MAY have fixed this in 1.6, but I'm not sure.
Mobs are enemies, so I suppose that there wouldn't have been.
No, mobs will not spawn in water or ontop of half slabs.
In Minecraft Classic, mobs can't spawn, so they can't exist naturally. If you play the Survival Test, and when mobs spawn there, you can save it and open it in creative mode so then the mobs can stay there. However, in Minecraft Creative Mode, mobs can spawn, but they can't hurt you because you have no healthbar.
no, some mobs can't, such as skeletons, creepers and zombies, but other mobs like spiders or endermen, climb over or just teleport in.
Yes, there will be other mobs! These include the Blaze, Magma Cube, and the Mooshroom. Also, other mobs will be added over time.
lynching mobs
They are called troops.
Yes, mobs can spawn on netherrack in Minecraft. In the Nether, hostile mobs such as ghasts, blazes, and magma cubes can spawn on netherrack, provided the light level is low enough and other spawning conditions are met. However, passive mobs do not spawn in the Nether at all.
Mobs are not at all good, as they can go out of hand and it will soon end in a riot.