Huge data transfer between respelsets in different zones

We have multiple instance on different zones and we can see huge volume like 150GB data transfer between two nodes when the data size is just 30GB.

We hosted the sharded percona mongodb on our eks cluster, where we have made sure that a master replica(rs0-0) and a secondary replica(rs0-2) lies in same availability zone and 1 secondary replica(rs0-1) lies in different availability zone making sure all three are o different nodes.

We have noticed a huge data transfer between these nodes, aro8nd 150GB . But our whole data size is only 30GB.

What could be possible reasons for the above cause as it is costing us a lot of regional bytes.