I do believe is had something to do with the development of the samurai class, the decline of Chinese influence due to China entering another divided period of its history

With collapse of the tang Dynasty

Also the local lords where gaining military power and in the 12th century the imperial throne lost all its power

Which would be held by the Shoguns from different dynasties until the Meji restoration in 1867

Like the British the Japanese don't have a problem with certain elements of hypocrisy we got no issues having a monarchy with no power

One reason I believe the monarchy is in declined is due to democratic idealism and younger generations being too literal

If China had a similar imperial system to Japan with the emperor being symbolic they might have been better off

It makes you think what would have happened if Cao Pi did not defran the last Han emperor

And his father Cao Cao never took the Imperial frown even after conquering northern China