Dads purchase baby-grows, bibs and duvet covers in their teams colours for their new born children, thereby signalling their intent that the child follows the same football team as they do. Why do they do this ? Possibly family tradition, fostering a commonality of interest and from a practical point of view, going to the same sports ground each week.
Leaving a religion or changing football allegiance can both cause family and social friction, and possibly result in being outcast from certain groups. However, changing the team you support or deciding your not at all interested in football doesn't lead to death threats and violence, additionally, it is common for there to be a variety of football teams supported by different members of the same family in a harmonious environment.
Also, unlike religions, marriage between supporters of different football teams doesn't require that one partner change their allegiance.
The other practical problem is that while interest in Football is growing across all communities, cultures and generations, interest Religion is on a rapid decline. Many people unthinkingly attend religious services through a mis-guided sense of duty to the older generations of the family.
These being the last generation in this world to be brought up in the absence of scientific information and the internet, and so have not necessarily enjoyed the luxury of freedom of thought or been encouraged to challenge 'social norms'. Once this generation goes, watch the church services empty, and this is why the fanatics are becoming more and more reliant on extreme child indoctrination in order to keep their 'congregations' viable.
So, it seems to me that in regard to CHILD INDOCTRINATION, FOOTBALL is far more understanding AND benign than RELIGION ever will be.