It’s simply the way it is.  The default alignment, in HTML, is not-justified, (AKA, left-aligned) and we are not able to override it.  Sorry!

We  actually can override that, by manually coding the lists, instead of using HTML list coding—but then, the line-wraps that currently work perfectly, aligning exactly right with the first letter of the first word on the first line, will no longer work that way.  They'll be "close, but no cigar," and each time a user changes their font size, the alignment would change. Smaller font? The line-wrap would move further toward the left-margin. Larger font?  Now it'll move further toward the right margin.  So...unless it's death-defyingly important, you want to use the default bullet and numbered list alignment settings.