Made birria tacos for the first time, they lacked a lot of depth. What did I do wrong?

The other day I made birria tacos for the first time and they lacked a lot of depth. I dont know what I did wrong. It was my first time eating birria so I'm not sure what it should taste like but from the videos I saw I just can't believe they would be so dull. Does anyone have any idea what I did wrong?

Here is the recipe I used https://www.seriouseats.com/birria-de-res-beef-birria-recipe-8362004