Repeatable accuracy is attained by the rifle, the ammunition and the shooter doing precisely the same thing every shot.
Most factory triggers are designed to be cost effective for the manufacturers and still do the job. Typically they are set to a poundage that is much higher than most people are capable of discharging a rifle with, without exerting enough pull that the rifle is effected. This has been called strangling a rifle to make it shoot.
This is done by the manufacturers to help avoid litigation from accidental discharges where bodily injury or deaths result. It is pretty easy for the manufacturer to disclaim responsibility when it takes 8 to 10 pounds of pull to discharge a rifle as this sort of force is then deemed "meaningful force".
The problem with this manner of trigger control is that the shooter has to put so much effort into discharging the rifle that the shots can get skewed. This makes it impossible to get the nice tight groups we are all after. The breaking point in many factory triggers is kind of all over the map so to speak, which makes consistent pull and discharge impossible.
The tolerances that most factory triggers are made to allows for the interchangeability of parts on the assembly line. How can this make for a great trigger? Simple, it can't.
Aftermarket triggers from the likes of Timney or Jewell solve the problems of repeatable let off and setting the pull weight down to low enough levels that repeatable accuracy can be attained, and most importantly, can be attained SAFELY.
In a Remington 700 for example, most triggers are preset at factory to about 6 pounds of pull, there is some creep left in the trigger on purpose. Replacing the factory trigger will not only completely eliminate the creep but allows for trigger pulls between 2 ounces and 3 pounds depending on the manufacturer.
Once you experience a high quality aftermarket trigger, chances are you will have all your rifles triggers replaced, they are THAT good.