Can someone please explain how seats are designated Medical Needs Specific.

I have a booking in October LAX to AKL Premium Economy and had requested seats in row 23 (row 22 was already taken) and got bumped (without notice) to row 26 which is alongside the toilets (not the place to be on a 13hr flight).

I know that seats requested are not final but what is the difference between row 23 and row 26 seats (apart fom the proximity to toilets) that would make these seats in row 23 Medical Needs Seats.

I contacted Air New Zealand and all I got from the 3 people, including the Customer Liaison Executive, I talked to/emailed was the automated response that seats can be designated for medical purposes.

I thought I would have got an explaination from the Executive instead of her quoting travel conditions.

I know that the people who got my requested seats deserve them but why could they not bump everyone down a seat row as I booked these seats early to avoid sitting next to the toilets in the first place and if they had told me earlier I could have changed to other seats before they were taken.

Sorry if this sounds like a whinge.