I agree with Marigold's view that a key driver in emigration was economic betterment (as it still is today with modern migrants). Ireland has very few natural resources (no oil, coal, iron ore etc) and so did not benefit from the industrial revolution in the 1800s, the way Scotland, England, the US, Canada & Australia did, which created hundreds of thousands of comparatively well-paid new jobs in new industries (coal mining, steel making, ship building etc). So that was a big pull factor.
There had also been a huge population explosion in Ireland going up from about 3 million people in 1750 to 8 million in 1830. There simply weren’t the jobs for all those people. In much of Ireland the only employment was subsistence farming, topped up in Ulster and one or two other areas with a bit of linen weaving. The famine was the straw that broke the camel’s back but people had been streaming out of Ireland in their hundreds of thousands, every year all through the century and they would have continued to do so, even without the famine.