Land generally was in the hands of the Aristocracy of England. Most still owned the land inherited from their families from the time of the first invasions of Ireland back in the 1600's.
Many were absent landlords, they had Estate Managers. Land was leased to Head tenants in many cases, then they had the sub-tenants in some cases down to less than an acre.
If you can figure out whose estate they lived on that might help.www.landedestates.ie
You probably would need to go to the Registry of Deeds in Dublin to go through land records, few are online.
Some are listed by donators on a website "Registry of Deeds-Ireland" on rootsweb. Just google and look for rootsweb. Go by surnames.
People often left for the better life that American seemed to promise, not much different from immigrants and refugees
today. In Wicklow for instance and the 95,000 acre estate of the Earl Fitzwilliam, had at least 1500 tenants. Once neighbours and friends started leaving for Canada others naturally followed. That estate had an Estate Manager and sub-managers, the land often leased in amounts of 500 acres to a Head Tenant who then had sub-tenants. This land was still in the family until the 1900's, plus they owned land in England as well, in this case Yorkshire. I don't think other estates would be much different.
There is more and more 'facts' available on the internet than 10 years ago but finding the answer to 'why' people left is a family story.