It's unrelated to post-processing. Moving the camera around makes things blurry at low frame rate (and 50fps is low) because of sample-and-hold blur. This can be mitigated by strobing the screen at the same speed as the frame rate, but few monitors support strobing at 50Hz (it would look annoyingly flickery) and if the game ever dropped below 50fps it would break the effect.

Blur Busters explains:

https://blurbusters.com/faq/oled-motion-blur