There's so much you can do with a scale.
Take the key of G major.
Sure, you can play it up and down as a starting place. Learning the fingerings for G major is empowering. But it doesn't have to stop there.
You can improvise new melodies with G major.
You can compose your own tune in G Major.
You can transpose melodies from G major to other keys.
You can transpose melodies from other keys to G major.
You can practice G major with different articulations.
You can practice G major in contrary motion (hands going in opposite directions).
You can figure out a tune by ear in the key of G major.
Come up with some more ideas on your own. I'm sure you have plenty.
A scale is more than a sequence of notes. It's more than a key. And it's certainly more than an exercise.
A scale is a whole universe of sound just waiting to be explored.