That’s because they are (or ought to be) providing a dinner.
The confusion is because the origin of the words lies not in where the meal occurs in the day, but what it consists of. Dinner was originally the main meal of the day, and might be had anytime between 11 am and 8 pm, or thereabouts, to suit your personal schedule. If you weren’t getting your dinner till the evening, then you’d have lunch – a light meal around midday, to tide you over. If you have your dinner around midday, then of course you won’t have lunch, but you may find you want something of the sort in the late evening – which is where supper comes in.
Status. Around the second half of the 19th century, midday lunch and evening dinner was the pattern for the suburb-dwelling, city office-working middle classes, while the urban and rural working classes, who generally lived within walking distance of work, would have a proper dinner at midday. It became seen as being “posher” to call the midday meal “lunch”, no matter what it consisted of, and the original definitions were partly lost.
When I visited a Sheffield friend, we had tea, which was what I would call dinner, and involved meat and Yorkshire puddings and no actual tea. How does that fit in?
I’m a transplanted Yorkshireman. Also I’ve heard that inside toilets are unhygienic and make you soft.