iptables : How to apply masquerade while pinging from DUT to outside network

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iptables : How to apply masquerade while pinging from DUT to outside network

My Device is connected to eth1 interface of the host and eth0 is connected to network.
Now when I am pinging google.com from device after executing below commands on host
sudo iptables -t nat -A POSTROUTING -o eth1 -j MASQUERADE 
sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE

I am seeing in wireshark at eth0, that during ping request source ip changes from DUT ip to host ip (i.e eth0 ip)
but that does not happen while ping reply , destination IP remains host IP only.
Why does it not show DUT ip as destination IP , Technically my final destination is DUT

For example:
host IP is x.x.x.x
DUT ip is y.y.y.y
pinging from x.x.x.x

on wireshark:
ping request  x.x.x.x to google.com -----> this I understood that it is due to masquerading and NAT
ping reply google.com to y.y.y.y expected but I see google.com to x.x.x.x   -----> why no Masquerading here?

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