Earlier quoted context omitted.
> Dump #datacenters - they are not critical Internet infrastructure! what is the alternative? I don't think self hosting is a robust/defensible option for a majority of internet services
Nobody hosts datacenters in Ireland because of capacity reasons. It's not a good location for power, people or connectivity. They host them there for tax reasons. You can bet your firstborn these datacenters are only the exact size that is the minimum allowed by tax law, not a square millimeter more. Yes, datacenters are critical internet infrastructure. But in Ireland they're more like a sailing ship with the sails…
It is, ah, probably about the best location if you want connectivity to both the US and continental Europe (and also, oddly, Japan, via an arctic cable). A big fraction of total transatlantic connectivity goes through Ireland, and there's substantial redundancy.
However, realistically, today datacenters are mostly built in Ireland because there are already datacenters in Ireland. There are no significant tax benefits to building them in Ireland vs most other countries, power is more expensive, and planning is more difficult (a lot of proposed datacenters for Ireland are now being refused planning, due to either grid constraints or dirty backup power arrangements). But, say, eu-west-1 is the biggest European AWS region, so why, as an Amazon customer, wouldn't you use it? (This is also a thing with us-east-1, which I think is still their biggest region despite their attempts to nudge people away from it to east-2...)
Expansion by _existing_ datacenter operators, who came in ages ago when the connectivity advantage was more of a big deal, seems to be the major driver. I don't think anyone who doesn't already have datacenters in Ireland is trying to build them; these days there are other locations with appropriate connectivity, cheaper power, and less fussy regulators.