Here's why:
* Adjectives describe nouns. "Lowest" describes the noun it modifies, telling us about its position on a scale.
* Verbs show action or a state of being. "Lowest" doesn't describe an action or state.
For example, you could say:
* "The lowest point on the map is marked with a red dot." Here, "lowest" describes the "point."
If you want to use a verb related to "lowest," you could use "lower," which means to move something to a lower position.