Just a matter of simple leverage. If you have a 2" distance to the middle of the trigger, and a 1/4" from the pivot point to the sear bar contact you have an 8:1 advantage. If it takes 8 pounds to trip the sear your felt force will be 1 pound. If you move the sear contact 1/8" further out, the ratio is 5.33:1, and the trigger pull weight will be 1.5 pounds.
The tumbler notch has some distance to travel before it goes over the edge and trips. In the first example, if the distance is 1/32", then the trigger (where your finger is) will need to move 8/32" (1/4"), and in the second example 11/64".
To my mind, the term "trigger creep" has to do with the amount of distance the trigger has to travel before the sear trips. So, in order to decrease trigger creep, you need to shallow up the amount of distance the sear has to travel. But, the shorter the distance the easier it is for a jarring of the gun to knock the sear out of the notch. Maybe I am misusing the term trigger creep though.
The sear spring pushes the sear bar down with some force in order to get the lock to positively click in to the tumbler notches. I have to confess I have not done trigger pull experiments both with, and without the sear spring installed to see what the difference is, but in pulling the trigger with an uncocked lock, it feels like about 2/3 of the force necessary to trip a cocked lock.