Because the incidence and effects are much lower than those dwelling on it would have us believe. It's not no concern, it's just that we're not psycho about it.
Probably because the "ruling elite" who are mainly Dems won't investigate.
From what I've read defective machines have been removed. If there's no evidence of defect, the most logical alternate reason would be voter error. So far the fraud angle has been accompanied by nothing but innuendo. As everyone should know, polls are staffed by poll watchers of BOTH parties. Real fraud would not be able to avoid investigation.