[Q] mount -o rw,remount not permitted topic

Code:

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C:\Users\Vitaly>adb shell
shell@thor:/ $ su
su
1|shell@thor:/ $ mount -o rw,remount /system
mount -o rw,remount /system
mount: Operation not permitted

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4.5.2 root by @p1gl3t
bootloop cause renaming DeviceSoftwareOTAContracts.apk_
and now some panic) why "not permitted" ?