They just have uninterested, untrained staff usually which results in not paying attention to product and not serving it right. Pay is vastly below what other bars pay in Dublin so they get kids - none of which have ever used a hand pump if they've even worked in a bar!
Guinness actually have a huge amount of failed products even within recent enough memory. When I started drinking, there was a "white Guinness" called Breo available which I remember quite liking. It was already basically dead at that time and vanished before I was actually 18.
There was also...
Still disturbingly popular in Northern Ireland. Was generally withdrawn bar a few holdouts in ROI last year for a new "IPL" of sorts called Hop House 13 which is significantly better.
Kaliber, basically Harp boiled to take the alcohol out - or at least it tasted like it. Mostly killed by Becks...