Why is it so difficult to score headed goals in Career Mode FC25!

You aren't alone in this.  I have 2 center backs that are 6'4" and 6'6" jumping and heading stat is high, and I have yet to make a headed goal.  I'm in my 5th season and have played just about every single game of every season

P.S.  I just had a thought as I responded here.  Maybe you are supposed to time tapping the shoot button as the ball approaches your head, instead of tapping shoot when the ball is being delivered.  I'll give it a shot and check back