Why is it that higher concentration of primers than the DNA template in PCR will favor the annealing of a template to a primer?
To simply put it, higher concentration of primers means more primers in the mix, therefore more chances of it annealing to your DNA template, however more is not always good. The optimum concentration of primers in a PCR reaction is between 0.1 and 0.5 µM. For most applications 0.2 µM suffices. Using very high concentration of primers can be troublesome as it can cause your primers to bind to partially complementary sites resulting in non-specific PCR products.
Using high concentration of primers ensures that after denaturation template DNA binds to primers instead of binding to each other. Also higher primer concentration enhanced product yield, as primers act as limiting factor for annealing.