Because even as late as 1861, Guinness made up less than 50% of Irish beer exports. Though by the time the 19th century ended, they had risen to three-quarters of the total. Why did this happen? How did Guinness come to dominate the English market for Irish Stout?
I think it's all down to branding. One of the interesting features of old newspapers are the adverts for beer. From the 1850s there are plenty of mentions of Dublin Stout. But here's the strange thing: often there's to indication of the brewery that produced it, other than that it was presumably located in Dublin.
There's one exception to this. Guinness. Who are often mentioned by name. It looks to me as if they've taken a generic product - Dublin Stout - and made it their own. Effectively making Guinness synonymous, at least in England, with Dublin Stout. At least that's my theory.
|Guinness exports to the UK 1861 - 1901 (bulk barrels)|
|"A Bottle of Guinness please" by David Hughes, pages 276-279|
|"Ireland Industrial and Agricultural", 1902, page 457|