According to the authors of the book Fidget to Focus, they make the argument that our brains are actually hardwired to not be focused.
It has an evolutionary explanation. Back in caveman times, if you were too focused on, say, weaving a basket or some other repetitive task, you might not notice the cougar sneaking up on the rock behind you.
Read and watch the full article here:
https://answerswithjoe.com/can-a-fidget-spinner-make-you-smarter-answers-with-joe/