Imagine a town that has 100 cars in it and 10 traffic deaths per year vs a town that has 10,000 cars in it and also 10 traffic deaths per year. Both towns have the same population. Without any sort of normalization the towns look the same, but clearly very different things are going on in those scenarios and a per mile or per car or whatnot will help you identify that. Obviously it doesn't give you any sort of root cause but it is an indicator that a deeper investigation is needed.
Human life being valuable does not change that certain activities carry a certain amount of risk, and so of course the more you do that activity the more likelihood the risk manifests. It is valuable information to know if one area has a hugely disproportionate number of traffic deaths compared to overall traffic metrics.
e.g. let's say I'm picking between two cities for my next job. Every day I will drive 25 miles to work, regardless of which city I choose. I look at the stats and see that in X city, there is 1 traffic death per 10,000,000 miles driven. In Y city, there is 1 traffic death per 100,000 miles. Therefore if I live in Y city I am 100x more likely to be involved in a fatal traffic accident. That is very relevant info to me and doesn't cheapen the value of human life at all.