Scouts stopped being single sex because it had too.
There were not enough leaders, and certainly in my area not enough boys wanting to go. We had all male cadets and no Scouts.
Scouting only survived because mum's helped and sisters and their friends joined too.
It's a situation that looks, slightly odd today, but it's not so long ago, that all football and cricket clubs were boys only.
The plethora of swimming, dancing, drama, gym, trampolining and other sports clubs did not exist.
In rural areas, like mine, schools did nothing after hours as we relied totally on contract buses to get home.
If a girl wanted to do something, especially at secondary age, Guides was it!