It was not like that in the London suburb I grew up in in the 80s. I think it was more common in smaller and poorer towns - maybe because people had less space at home. I agree the age gap probably affects it a lot. Keeping an eye on a younger child at home with help near by is very different from going out.

Kids spending a lot of time in front of the TV was already a concern in the 80s so screen time was definitely a problem back then. IIRC the average amount of time children spent watching TV a day was about five hours a day in the UK.