Maybe you both got vetted but only as much as the Gardai felt needed doing. In Dublin, the carriage office does it for hundreds of drivers and it's probably pretty automated. In rural areas, it might be a bit more personalised and involved and they might even know the applicant.
Maybe most taxi drivers have pretty boring lives - they just grew up in the their parent's house, moved into a bedsit for a few years before they got married and bought a house and had 2.4 children. There's not much vetting you can do on that!
But if you were lived in a foreign country and got your start in a cash business like betting (colourful characters), maybe there's a bit more digging to be done on that?