Older technology used to present flight levels as altitude derived though FMS or Transponder.
Newer technology can use GPS of aircraft or an internal one.
Neither technology makes correction for QNH like an altimeter.
Hence when flying level below transition you can see all wonderful manoeuvring altitudes displayed. But as aircraft is then generally climbing or descending it doesn't really matter to passengers, plus the system always lags a little as well.
Maybe you can remember on your recent flight, that the passenger display is always in even feet or equivalent meters in cruise, but depicting the flight levels flown as a constant not as an actual corrected altitude above ground, but advertises it to passengers as "altitude".
So the display in the cabin is always annunciating the "flight level" as an "altitude".
Think the initial system design is not taking into account people reading too much into the system discrepancies with adequate background knowledge about pressure changes etc. Made for Mr & Mrs Smith to tell them how high they flew in cruise to XXX.