Roughly 90% of England prescriptions are free, made up of the under 16s ( under 18 if in full time education), the over 60s and people on benefits. England has a population of about 58 million, Scotland 5 million, if like England 90% are entitled to free meds this would mean only 500,000 would be paying for prescriptions, the cost to administrate paid for prescriptions would negate any benefit hence all get free. It is also worth remembering England, Wales and Scotland have separate run NHS.
The devolved countries made the choice to spend money on Health and Education, England with its much bigger population has decided that there is other priorities
Edit
If you want free prescriptions you could always move, but be prepared to pay more council tax, food and fuel bills.