I think the problem is that when an arrest is made, by calling it a hit & run, you essentially tie the alleged (that word again!) culprit to the actual crime. They become linked and it appears to make him guilty, before he or she has been judged in a court of law. 

In general, with the kind of litigious society we live in, you can't be too careful. So they are. I agree it sounds absurd. (You'd never hear "alleged murder.") But in a world where people will sue for millions at the drop of a hat (an alleged drop of the hat!), news organizations can't afford to take that chance. 

The TV station where I worked was once sued for a story I wrote. I got the info straight from the reporter who covered it, and he was 100% sure of his sources. So we put it online and the federal politician it was about immediately called, demanded it be taken down and an apology issued and oh, by the way, she was suing us.

We did take it down - temporarily - while the company's legal team looked it over thoroughly. In the end, I think we were in the right, but they paid her some money because it would have cost more to litigate the case (which we would have won) than to just give her the money to go away. No admission of blame was ever attached.

Happens a lot these days, which is one reason people are so lawsuit-happy. So the word "alleged" becomes your best friend. 

RadioActive has summed it up well. When a suspect is charged with a crime, they're basically innocent until and unless proven guilty. For any entity or even individual to claim or maybe even insinuate (imply) that someone's guilty when they haven't been proven so could constitute slander and/or libel. I'd imagine that the potential negative attention from other news sources and/or social media and the "concerns" that could stoke amongst advertisers might be another at least feared threat.

They're not using it appropriately, they're using it to cover their asses just in case.

Saul wrote:

Binson Echorec wrote:

They're not using it appropriately, they're using it to cover their asses just in case.

And I'm not sure that legally really does cover their asses...

I'm not sure either, Saul, but I'd bet today's less nuanced journalists think of it as a "safe word".

The suspect's guilt is allged. The crime is not.

Well, this is an "alleged" society where people are innocent until proven guilty. You may not like it, but I am fairly certain you would hate the reality of turning that sentence around.

This is one that has troubled me for years.  There was not an "alleged"  bank robbery.   The bank was either robbed or it was not.   As well, I was always taught that the word alleged involving a suspect or charges offered no protection from legal ramifications.   
The other one I have wondered about is the phrase "charges have not been proven in court."   I do not remember ever writing that phrase, but notice it being used regularly.   I don't understand why.  If a suspect has only been charged at this time of course the charges have not been proven in court.
Any clarification would be appreciated.