Why are American carrots so skinny?

I know this is a weird thing to ask, but google is failing me and I don't have enough agricultural knowledge to know where to start looking. I'm hoping this isn't another food thing I'm the only one who thinks about.

I love carrots but I'm increasingly irritated by the tiny long carrots that I can find in the markets. I just bought a bag of carrots that had a number of them thinner than my pinky finger. In the meanwhile whenever I look at cooking shows on Youtube that are made in other countries they have thicker, longer, or otherwise more substantial carrots. The ones in Japan seem huge; some of them look like they have a 2" diameter!

Is it just that they are using a different variety? If so, why would they be using those tiny ones here?