I think some of it is due to a huge surge in everyone being diagnosed with something and wanting a quick fix.
Lots of coverage on tiktok about ADHD, so now lots more adults are getting assessed for ADHD then requesting medication.
Similarly, lots more media coverage of menopause these days so more women are going to the GP about menopausal symptoms and requesting HRT, hence GPs are running low on that too.
Depression, anxiety etc are on the increase and the funding for counselling is not there, so tablets are a quick fix to get people back out the GP's door. More prescriptions use up the stock, hence supplies run low.
FWIW, many, many studies have shown that exercise and improvements to diet are the best way to treat a number of physical and mental health issues, but people are often not willing or are unable to put in the effort, and prefer to rely on pills.
So to answer your question, society as a whole is responsible for the missing drugs, because people would rather be medicated and feel that there is nothing else they can do to change their situation, than get up off their bums, run around the block, stop eating family-size chocolate bars/bags of crisps, takeaways, booze, fizzy/highly caffeinated drinks.