Why are so many words in ancient calligraphy written obliquely in the upper right corner?

Real calligraphy is not writing square characters, but writing good characters.

China's calligraphy is extensive and profound. In the eyes of laymen, square and well-behaved words are good words. In fact, the real good words are: happy and calm, indulgent and measured, flexible and powerful, flying and simple, broad and heavy, moist and powerful, unrestrained and accurate, strict and loose and dense, graceful and vigorous!

Only when these standards are truly met is a truly good word! And this can't be achieved and experienced overnight.

I hope my answer is helpful to you!