It is because these Asian have inferiority complex. Being subservient to Western dominance for over 100 years, it will take a long time to get rid of this mindset and build the confidence in China as the protector of Asia. Remember we used to play that role until the West came and took it away from us. We were powerless to defend as we were backward and didn't believe in new modern technology can decide geopolitical fate. These Asian states like Philippines, Japan, and Vietnam have saw and were dominated by Western powers for so long that they don't believe they stand a chance to fight back. They don't trust our capability yet as realistically, we are still behind the West so I don't blame them. We just have to continue to build on our strength. Expect 2020s for many major breakthrough. That is the decade you will see major shift in Asia confidence.
Once China becomes considered a peer to the US, both economically and militarily then the mindset will change. This will be obvious to all sometime in the 2020s.
Also at this moment in time, some Asians think that Indian can somehow "balance" China. A country like India, that is made up of many nations, can never challenge a unitary state like China as it's primary focus is on keeping itself together rather than pushing it's economy forward. In the 2020s while India is still very much a 3rd world country China will look and feel like a 1st world country and then all these Asians(even the Indians themselves) will realise that China is in a totally different league to India. Once this happens, even the proud Japanese who I respect for becoming the first Asian country to industrialise will accept China's place as the leading nation in Asia.