Simply because nobody has successfully pitched the Unicode group to add one.

Anyone can pitch new emoji, they just have to go through the fairly easy but strict formal process.

I was looking for a pirate emoji like 5 minutes ago. I'm sure it's not the first time but I'm super surprised that still isn't in there. Seems so obvious.

Well there's a pirate flag

What’s next, a cowboy emoji? A ninja emoji? But seriously, as much as I like emojis, I kind of feel like they should stick to emotions. Maybe other intangible things. They’re hard to convey verbally (and succinctly), simple concrete nouns are good for a bit of fun and for UI icons, but really not very useful if we’re being honest. Unless you’re texting with a lizard, or my lazy elementary-school niece who shouldn’t really have a phone anyway…