These restaurants all hold full pub licences - I am not intending to tick off everywhere with a Special Restaurant Licence (hereafter SRL) that allows them to sell the full range of alcoholic drinks.
Some of them are in former pubs that have since become restaurants, e.g. S0297 Daata in Blackrock is in a building which has had many pub incarnations, and there has been a licence on this site for likely over a century. The other branches of the now expansive Daata chain do not hold pub licences.
But rather a lot of them are not, and instead bought in a pub licence on opening, or at another time afterwards. Pub licences are not cheap - depending on demand they can range from €45000 upwards, and have reached over €100k in the modern era (and one traded for over £1m in the old era where they could not be moved far easily).
Pubs do this because it is significantly easier to have a conventional bar with one. A SRL limits how you serve drinks - table service only, when you serve drinks - limits before and after meals and on the minimum cost of meals, albeit that cost is now extremely low, and to who you serve drinks - only those actually dining.
Possibly more importantly than all of these issues for many restaurants, is that SRLs additionally place onerous requirements on what food and drinks you serve.
The food requirements are very traditional including a requirement to offer soups and meat main courses; and for drinks bar must have an "adequate wine list" on a physical wine menu presented to diners, and offer both spirits and beers "of Irish origin". So no Asian restaurants serving vegetarian food with only Asian beers allowed then! I somehow suspect these rules are not enforced to their full extent anymore, but the SI is unamended and in force to this date.
The regulations go so far as to define the types of chairs (must be cushioned) and tables (if no tableclothes, they must be polished hardwood with table mats) a restaurant must have, that the restaurant has a cloakroom, that it has gendered toilets and that "table appointments" - everything on the table like salt cellars, candles, etc - match between tables. Basically you need a prim and proper 1980s Irish restaurant to comply with the rules.
I have also seen claims elsewhere that a SRLs doesn't allow draught beer; but I cannot find any legislation to back this up; and I believe it is a conflation of how you are not allowed have bar service. Draught taps does not equal bar service, but it would certainly conjure up images of such.
You can also apply for "late licences" - special exemption orders - to serve alcohol at later hours should you have booked a function that requires this, which cannot be done on a SRL.
So a full pub licence makes for a much easier time actually serving whatever alcohol (and food) you want to serve in a restaurant.
A recent visit of mine to 1022717 Ivy Asia shows multiple reasons why - they do not serve any beer of Irish origin, their food menus do not match the late 80s Irish idea of "proper" as specified in the SI, and you can stay drinking cocktails for quite some time after you've finished eating if you so wish. I'm pretty sure the "table appointments" weren't identical on every table either.
Restaurants that have gone down the route of getting pub licences range from relatively high end places like both Ivy branches and the nearby Dunne & Crescenzi, through to fast casual places like Captain Americas, and when still trading, TGI Fridays.
The in house restaurants of the Brown Thomas and Harvey Nichols department stores, multiple restaurants in the former Press Up empire and odd dual uses like the Malahide Siam Thai's small cocktail bar and the now gone Dundrum Donnybrook Fair doing off-sales as well as its restaurant make up the bulk of the rest of the pubstaurants. Not all of these places welcome non-dining drinkers; but plenty do - as you can see from my many writeups on here. I may go back and tag them all as such in future.
