There are smaller carseats which are less likely to interfere with reclining. There are bulkheads. You can put a family member in a seat with obstructed reclining.
Seats do not have to be installed rear facing in aircraft - typical guidance is for cars. 5 yo definitely does not require a car seat on a plane.
It is parent's responsibility to be considerate but unfortunately too many take a position that the world revolves around them.