Sadly roadkill usually doesnt die quickly, which leaves plenty of time for the body to put out all sorts of chemicals like adrenaline and shit which makes the meat taste worse. Im no expert at all but ive heard a few tines from hunters that an instant kill is important for the quality of the meat.

https://www.grandviewoutdoors.com/gear/hunting/can-better-shooting-lead-better-meat

The livestock industry has known since the 1970’s that animals experiencing stress prior to slaughter undergo metabolic reactions. These reactions can reduce the quality and taste of meat. The same principles apply to wild game killed in the field.