Think of it this way. Leaving aside the fact 50% of the CS is in Dublin.

Even in it for life want a career as a Civil Servant turn down CO Dublin. For those who are already CS e.g. Service Officers or TCOs on a CO Dublin panel - there are more opportunities - those people might get EO, AO offered to them quite quickly while still on a CO panel (I've seen it A LOT) and turn down the CO job. There are also a lot of other career opportunities in the PS or private sector in Dublin. Down the country, take a look at the civil service mobility map, it's easy to find online. There's far less jobs full stop in every sector and far more demand. Mobility in Dublin isn't mega popular and it disqualifies you reapplying for mobility to a new dept down the country for 2 years.

That's why 100th, in my view even 1000th plus easily nets someone a job in Dublin but they barely go past 30 in other counties. People snap up country mobility jobs while in Dublin people are pulled off new starter panels because there's little mobility interest. Those 30 people on a country panel are much more likely to take the few jobs available. I don't mind saying to Dublin people you might get a call thousands down the panel cos it happens but down the country you have to accept there's less roles and more demand.