Why do defenders pay too much attention marking the opponent during set pieces

Why not target the ball and be the first to it?

When you focus too much on the opponent you are reacting to everything but if you get to the ball fisrt then you can head the ball out of danger before your opponent does anything with it

Look at Portugal, Ronaldo who is their best player in heading the ball defends the first post to make sure he heads the ball out of danger first

Why can’t Simy Nwankwo do same for us and defend the first post?

Egypt vs Uruguay - set piece goal 1-0
England vs Tunisia - 2 set piece goals 2-0
Croatia vs Nigeria - 2 set piece goals 2 - 0

I think even the 1 goal score by Poland against Senegal was a set piece goal

Omeruo and the defence did well on set pieces today

Attack the ball, get to the ball first and your opponent can’t do much

In the game against Croatia we were chasing the opponents too much

Against Iceland our defenders were attacking the ball and were first to the ball and hence why we won the battle on set piece was won

We have to maintain this concentration level