Nodes stats API CPU usage value is -1

Hello, I have a question.
I have installed elasticsearch on azure. OS is Ubuntu.
And look up the cpu usage.
I ran '_cat/nodes?format=json' , and the cpu value is -1.
can not understand.
I browsed the documentation (Nodes stats API | Elasticsearch Guide [8.5] | Elastic)

(integer) Recent CPU usage for the whole system, or -1 if not supported.

In what cases is this not supported?

please answer about my question. thank you.