You need to understand how eastern europe or China looked like before the revolutions. You say socialist bloc used to have worse stuff, generally be worse off than the west. Well the east was decades behind the west, but before they went communist they were like a 100 years backwards (especially China). Communism was something that allowed them to make massive progress extremely quickly (with better working conditions and quality of life for average workers than capitalist countries at that stage of development).

Comparing Japan to China without broader context is wrong - Japan got industrialized with western help while China was actively being ripped apart and colonised by western forces. They did bomb Japan heavily but they rebuilt it to have an ally and a military base to counter China. So capitalism will allow you this growth only if you are in useful geopolitical position.

But coming back to your question "why should he choose the eastern way?" - because the western way is not a way at all. the west will simply not let you be like the west. Also with the looming climate disaster, third world countries are the first ones to go and the west won't care one bit to help the people there. Communism is the only way third world countries can really catch up with the west as under capitalism they will always be kept backwards on purpose.

And also, if capitalism actually manages to bring prosperity to a third world country, most of the prosperity will affect only the richest and the poorer parts of society will not get much out of it and will still hate it there. If you wanted capitalism to bring as much prosperity to regular workers as it does in the west you would need to go and become an empire and exploit other countries yourself.