Why was process of modernization slow …

It is important to note that the transformation of social and political institutions and daily life was pot just a question of reviving traditions, or tenaciously preserving them, but rather of creatively using them in new and different ways. 
For instance, the Meiji school system, modelled on European and American practices, introduced new subjects but the curriculum's main objective was to make loyal citizens. A course on morals that stressed loyalty to the emperor was compulsory.
Similarly changes in the family or in daily life show how foreign and indigenous ideas were brought together to create something new.

The Chinese path to modernisation was very different. Foreign imperialism, both Western and Japanese, combined with a hesitant and unsure Qing dynasty to weaken government control and set the stage for a breakdown of political and social order leading to immense misery for most of the people. 
Warlordism, banditry and civil war exacted a heavy toll on human lives, as did the savagery of the Japanese invasion. Natural disasters added to this burden.