H. C. Brown has suggested that the halogen atom does add but, at high temperatures, is expelled before the second step of free radical addition can occur$^1$.
Addition of halogen atom gives this radical, which falls apart to regenerate the starting material if the temperature is high or if it does not soon encounter a halogen molecule to complete the addition. Hence, low concentration of halogen can be used with high temperature to favour substitution over addition$^1$.
The allylic radical, on the other hand, once formed, has little option but to wait for a halogen molecule, however low the halogen concentration$^1$.
For the formation of minor product you may look into this question.
To follow the Markovnikov's or anti-Markovnikov's rule, there should be difference of electronegativity between the two atoms. Therefore, I do not understand what you are trying to ask.
- Organic Chemistry- Morrison and Boyd (6E); Page 389-390