grammar - Why is neither て nor ます form used here?

For full context: https://www.satorireader.com/articles/sanzu-no-kawa-episode-1-edition-m

The sentence in question: その日の朝は、いつもと全く変わらない、平凡な朝だった。

My attempt at translation: "This days morning, really as always nothing changed and it was an ordinary morning."

I usually would expect 変わらない to be either て or ます form to formally connect to the noun 朝 which it modifies. But instead, it's just plain form. Did I miss out on something, or is this just a question of style?

Answer

This is simply because いつもと全く変わらない is a relative clause that modifies 平凡な朝. Of course a relative clause does not end with て/で/ます. Don't be misguided by the comma :D (Alternatively, you can think いつもと全く変わらない and 平凡な independently modify 朝.)

その日の朝は、いつもと全く変わらない、平凡な朝だった。
It was an ordinary morning that was no different than usual.