Because while there are those metal gages for suitcase size, no on makes you run your bag through them before boarding. The system mostly works on the honor system.
Police should have been summoned, the woman arrested, and the plane could have taken off less than 30m late.
Ryan Air has it covered.... just charge a lot more extra money for oversize bags and enforce it strictly...:^)
Check out the costs -
https://www.liligo.co.uk/travel-magazine/flying-with-ryanair-the-low-down-on-luggage-21541.html
I travel with a “carry-on” size bag and it bugs me when other passengers roll down the aisle with giagantic bags that are nowhere close to fitting under the seat as required.