Why are pharmacists so weird about selling ovex for threadworms?

Needed some ages ago and a pharmacist wouldn't sell it to me as I had symptoms but hadn't visually seen the worms (my reply was that's not an area I visually inspect). I had to get the GP to prescribe it.

Was chatting to two friends in the pub recently who both described difficult experiences buying the medication. Having to go to multiple pharmacists or the pharmacist appearing reluctant or concerned about selling it.

We couldn't work out why, it seems safe and doesn't have any potential for abuse as far as I'm aware. What are we missing?