Why aren t McDonalds fries vegetarian?

The suppliers that produce and pre-fry the potatoes before freezing and shipping, use a beef flavoring that contains a dairy product.

Taste - frying them with a "beef favouring" makes them more tastier for the customers and hence they will come back for more.

Oh, there is a whole story about it. And this is somewhat old news. I can't remember the details but I'm sure there are still some articles about it on the internet.
So from my memory. some vegan group discover that McDonalds was adding some kind of beef flavoring to their fries. There was a pretty big stink about it and again this is just from my memory - but the big deal wasn't the beef flavoring - the big deal is that McDonald's lied and then continued to lie.
Supposedly McDs stopped using the beef flavoring but if you go to the McDs FAQ page you will see that McD's no longer claims its fries are vegetarian.

Beef flavoring I think

Its potatoes - not meat. Hence, the fries are vegetarian.

The fries contain beef favor, so not vegetarian.

They are, I thought. They are fried in vegetable oil... Unless they have some random animal additive?
They do have a wheat derived ingredient, I know that.

It varies apparently from country to country but to make it easy they do not classify any of their fries as vegetarian or vegan. For example, they contain natural beef flavor in their fries in the US as well as dairy which makes them neither vegetarian or vegan. In Canada apparently they do not use the natural beef flavor or the dairy in the making of fries which would at least classify them as vegetarian but they do not guarantee this.

Cause they are fried in fat that is not vegetarian friendly.
Ps not a tattoo question.

The potatoes themselves are "vegetarian" because they're vegetables. I think you mean vegan, which means the cooking process includes oils and additives that aren't vegan (e.g., cooking them in lard as opposed to vegetable oil).