Why can't I ping 127.0.0.1 from some network interfaces?

I'm on OS Sierra. This is (part of) what I get on ifconfig

...
en0: flags=8863<UP,BROADCAST,SMART,RUNNING,SIMPLEX,MULTICAST> mtu 1500
    ether 98:01:a7:b4:91:63 
    inet6 fe80::4e:52ae:9fa8:2e6c%en0 prefixlen 64 secured scopeid 0x5 
    inet 192.168.1.33 netmask 0xffffff00 broadcast 192.168.1.255
    nd6 options=201<PERFORMNUD,DAD>
    media: autoselect
    status: active
...
utun1: flags=8051<UP,POINTOPOINT,RUNNING,MULTICAST> mtu 1400
    inet 10.161.136.55 --> 10.161.136.55 netmask 0xffffffff

If I try to ping 127.0.0.1 from en0 interface (command ping -S 192.168.1.33 127.0.0.1) it works fine, but if I try to ping it from utun1 (command ping -S 10.161.136.55 127.0.0.1) I get a timeout. Why is that?

Actually, I had a look at netstat and saw this:

Routing tables

Internet:
Destination        Gateway            Flags        Refs      Use   Netif Expire
10.161.136.55      10.161.136.55      UHr            65      550   utun1
10.161.136.55/32   link#14            UCS             0        0   utun1
192.168.1.33/32    link#5             UCS             1        0     en0
192.168.1.33       98:1:a7:b4:91:63   UHLWI           0        9     lo0
...

Why do addresses 10.161.136.55 and 192.168.1.33 have such different configurations for the netif column? How do I change them? I'd like to change line 10.161.136.55 to use netif lo0