In my opinion, I think Irish people have a deep distrust of Irish banks, are reluctant to put money on term deposit with them, and are happy to make do with a small nett loss in return for the perceived comfort of being able to get their money out immediately when things go wrong.
It's not just rates that are important though; for example, to avail of the current best term deposit rate from an Irish bank, I would also need to open a current account with them, which I don't need, and which would incur charges, paperwork and other bureaucratic overhead. With Raisin, as a once-off, you open a single free account using a smartphone and can deposit in any of dozens of EU and EEA banks with absolute ease, while also getting better rates. (yes, there's the tax return, but that's only a downside if you don't already do one each year).