I've noticed this too. It's a disheartening state of affairs, and incidentally not restricted to The Hatters: I could name quite a few Marple pubs which just a few years ago would be thronged on a Friday or Saturday night but which are largely empty these days. I've been re-reading topics in the 'Recommended Pubs & Restaurants' section, and about five years ago someone wrote about one pub saying something along the lines that the queues at the bar 'were 15 deep'. You would be hard-pressed to see that level of demand today.
By chance, I was on the Robinson's Recruitment website earlier and I see The Hatters is available as a tenancy:
http://www.myrobinsonspub.com/vacancies/vacancy/110.
The Midland and The Norfolk Arms in Marple Bridge - not Robinsons pubs - seem to be constantly busy. It's certainly true that one can find oneself waiting several minutes to be served there. And maybe that's the key: in my more contemplative moments I have found myself wondering if brewers actively need pubs to under-perform so they can offset losses against tax liabilities.
Looking more strategically at the Marple pub scene itself I find it notable that almost every one is owned by Robinsons. That's quite a level of saturation. I firmly believe that Marple needs a prominent non-Robinsons pub - Sam Smiths or Hydes, say - to reverse the decline in Marple's pub footfall. Robinsons might not be in favour of this idea but I feel it would actually re-invigorate the Marple pub scene as a whole and Robinsons pubs would see uplift in sales as a result.
A note to 'admin': should this topic not be moved to the aforementioned 'Recommended Pubs & Restaurants' section?