As a French, my guess is simply that the brand is not price competitive and up until now, they didn't have the right marketing to justify the higher prices.

Duralex is a beloved brand, and the French wouldn't like to see it go, but not enough to have much of an influence in the shopping aisle. The nostalgia aspect is real (ask the French about the numbers at the bottom of the glass ;) ), but it may be a negative when looking for more "adult" glassware. Maybe you don't want your guests or yourself feel like your are in a school canteen. School canteens also don't have a reputation for being luxurious to say the least, which may be a problem if you want to charge a premium. It may be that's the idea behind the pint glasses by the way. Show that Duralex can make glassware for grownups too.

A Danish supermarket had a loyalty program where you'd collect point and could get Duralex drinking glasses for the points. We got probably 25 of them, I don't think I'd consider buying anything else going forward, the quality is absolutely worth the minimal extra cost. You can get six for around €25EUR that is basically free.

I don't agree that they aren't price competitive, at least on normal drinking glasses.

Here you can buy 250 ml glasses for 1.39 Euro a piece. Even cheaper for sets. I’m not sure how cheap we need glasses to be?

Create a separate high-end brand, Duralux.

It is more expensive than for example IKEA glasses, but I swear by Duralex.

Ever since an IKEA glass spontaneously exploded on my desk.

I suddenly remembered we used Duralex at school in Sweden in the 90s, so I ordered brand new Duralex glasses and no explosions yet.

I imagine if they were being used in schools, with 13-17 year olds, being washed every day for years until they were covered in scratches, they must be pretty tough.

Yes, we had them in school in the UK too. Just had a flashback to the number at the bottom of the glass

The issue is that it is difficult to find a marketing justification for high prices in everyday glassware... nothing more like a glass than another glass and people are obviously not prepared to pay a premium.