I just wanted to add that it's also helpful to consider the origin of the test in the first place:

https://www.verywell.com/history-of-intelligence-testing-2795581

Specifically, it was invented to help the French government identify school children who needed special assistance. Binet himself (one of the inventors) actually believed that the should never be used as a single, permanent measure of intelligence - there's more detail in the article. Could be part of the reason it's not static and that we see it change in people all the time.

Good reply though, I agree with the points you bring up :)