Just my speculation but what 20 years was considered a „specialty coffee” now has nothing on the actual barista-run specialty places. And people learned how their coffee can actually taste like.
Not to mention the effect advocates like James Hoffmann must have had on people’s general awareness.
Also, poor people absolutely eat there. All those poor people working there get free food and employee discounts, others use the app, or they eat there once in a while as an alternative to more expensive restaurants.
Maybe I get that impression a little less in the UK, but that's only because their food isn't bad enough for British people to like it when they could be eating smack barm pey wet.
Also, by somewhat premium I mean in the same category as Starbucks, not a sit down restaurant.
That kind of worked back when the competition was Folger’s annealing to the pot at the local diner, but chains like Dunkin’ expanded and McDonald’s et al. upgraded and they all have better tasting coffee you don’t need to sweeten so much to cover the bitterness.