In England, up until a couple of weeks ago, masks weren't in the shops - not in the typical supermarket anyway. They were available online, though stocks of the normally priced stuff ran out fast, they were back in stock in late April - but online shopping does knock out a significant percentage of the population, and the sheer number of options will have put off some others.
The first time I saw masks for sale in a supermarket was in late June, in a B&M (don't judge - the catsan is cheap in there
) at £3.99 for 2 of the basic disposable surgical masks - yes, the sort that sell for 50 for £10 online. I suspect that when the regulation comes in we'll have a couple of weeks in which the big supermarkets give unmasked people a mask at a stall outside the door or ask for a charity donation or something. Eventually, especially if the supermarkets start selling washable ones for a couple of quid, the actual grown adults will take responsibility for themselves.
The government prevarication really hasn't helped - if they'd mandated it earlier, the habit would be there by now and the masks would be on sale everywhere. As it was, even a month ago, people were going to out-patient hospital appointments without a requirement to wear a mask, and without being given a mask at the door. Asking people to wear them routinely in shops now will have been a surprise to some people.