It's very simply explained by this being the most succinct way of wording it. Some methods of killing have verbs that suit mentioning the attacker - shoots, stabs. Some don't. "Rammed" or "runs over" isn't as precise as mentioning that a car was used, and adding "with car" makes it more awkward than it's felt to be worth.

Compare bombs. Very typical for a bomb attack to be "bomb goes off in crowd" or similar, rare for headlines to contort themselves with "terrorist plants bomb near crowd and triggers it to explode". But nobody worries about how such a construction assigns undue agency to the bomb and acquits the bomber; it's just linguistically awkward to mention him within the confines of a newspaper headline.