Passports not being checked at airport

[AccioCoffee]

Is this the thing now, I have traveled between Ireland and the uk quite a lot recently and not once was my passport looked at by staff in the airport or plane. People just showed boarding passes and that was it each time. Why do they not check them anymore even though it's technically internal flights.

You won't be checked between the Republic of Ireland and the U.K. as it's the Common Travel Area. Once you're in it, there are no passport checks.

https://en.m.wikipedia.org/wiki/CommonTravell_Area

A flight between the UK and Ireland (assuming you mean ROI) still isn't an "internal" flight. But yes, it's because of the Common Travel Area.