I have no idea why you think safety laws prevent people from playing conkers in spite of the very thread you are commenting on being evidence that people play conkers and it is perfectly legal.
I do wonder if by banning it in schools it will get less and less common till it disappears. I suppose you predictably think that's nonsense.
But pedantry aside, its banned for the people who used to play it most and enjoy it, at the place they did just that.
How could I be so clueless?
“What exactly are you so happy about?' Harry asked her.'Oh Harry, don't you see?' Hermione breathed. 'If she could have done one thing to make absolutely sure that every single person in this school will read your interview, it was banning it!”
The ban is generally lifted or just not enforced at all after a year or two.
For starters the playground monitors have more important stuff to do than remember the list of banned activities and try to enforce them.