Why can't WhatsApp write to bind mounts?

I moved all the data of WhatsApp to

/mnt/media_rw/6333-6461/WhatsApp

, where 6333-6461 is my external SD card. I opened WhatsApp to find that I could not open any previously downloaded data. This is expected. Now, I executed the following commands in Termux:

`
$ su
# mount -o bind /mnt/runtime/write/6333-6461/WhatsApp /mnt/runtime/write/emulated/0/WhatsApp

` When I opened WhatsApp, I could see all the data that I had previously downloaded. But now I cannot send or receive anything - all sending fails, camera access from WhatsApp fails, and downloading fails. Evidently WhatsApp is not being able to write onto the bind mount. Any solution to the problem? My phone, a Samsung Galaxy On7, Android 6.0.1, is rooted with Magisk 20.1 and running stock ROM.