Those alerts are pretty loud, particularly with noise canceling on. One of the things I love about noise canceling is I can listen to my music almost at zero volume on the phone. With everything else blocked out, it's plenty loud. Then the 'bloop bloop' happens and it's like someone hit me over the head.

I know a lot of people use airpods as like ambient sound, just keeping them playing super quiet all the time. I personally keep them at a moderate volume because I have no interest in hearing anything other than my music, but maybe the low battery sound is volume-independent, so people who listen at 10% would be jarred by it.