Why can't you summon an Ocelot or a Horse using a cheat code in Minecraft when you can summon wolves and sheep and stuff?

Answer 1

You can, actually!

You can simply spawn Ocelots and Horses, along with wolves and sheep with spawn eggs.

But, if you want to get technical, the general code for summoning mobs is

/summon (mob name) ~ ~ ~

But, some mobs, like Mooshrooms, Ocelots, and Horses seem to be unable to be spawned. This is because in the coding of the game, the have slightly different names, which is why people say they are unable to spawn them.

So, an Ocelot should be

/summon ozelot

And, a horse should be

/summon entityhorse

And here's a few extra:

to summon a wither:

/summon witherboss

to summon a snow golem:

/summon snowman

to summon an iron golem:

/summon villagergolem

to summon a baby zombie:

/summon Zombie ~ ~ ~ {IsBaby:1}

to summon a baby villager zombie:

/summon Zombie ~ ~ ~ {IsBaby:1,IsVillager:1}

to summon a Magma Cube:

/summon LavaSlime

to summon a Zombie Pigman:

/summon PigZombie

The other mobs are pretty straightforward to spawn.

(This is as of 1.8)