Because the cabin isn't pressurized to sea level pressure instead it to about 8k ft equivalent. (while the plane is 4.5 times higher)

This means there is less differential pressure than if the cabin was pressurized to sea level pressure. But it's still within the limit of what passengers feel comfortable with.

This answer on aviation.SE contains a plot of cabin pressure over time during a flight:

^Source

The composition of air doesn't change with altitude just the pressure. This means that you only need to compress the air before blowing it in.

Because the cabin isn't pressurized to sea level pressure instead it to about 8k ft equivalent. (while the plane is 4.5 times higher)

This means there is less differential pressure than if the cabin was pressurized to sea level pressure. But it's still within the limit of what passengers feel comfortable with.

This answer on aviation.SE contains a plot of cabin pressure over time during a flight:

^Source

The composition of air doesn't change with altitude just the pressure. This means that you only need to compress the air before blowing it in.