Two way to look at it … a) the banks are increasing their margins by reduced the rate at which they borrow from depositors while charging borrowers more or b) the banks are screwing their retail customers two ways.
The cost of funding is down over the last year. Refi rate dropped several times, refi rate going to drop again in June, Euribor down, Euronia down, deposit rates down, ECB LTRO / ECB overnights liquidity cost down in real terms and volume terms.
Plus they all behave like sheep. Only PTSB have increased variable rates very recently. A copy cat drop might happen but it would be unpalatable for it to happen anytime around the next ECB meeting.