I think they were trying to be generic over “flex-direction”, meaning that attributes like flex-align depends on the “direction” of the parent. It’s very rare that you change the direction and really benefit from that.
I don’t know if that’s the only reason, so I’m not gonna say it was a bad choice. But at least to me, I’m exactly like you in the sense that I can’t remember which one is which. I would have preferred either better naming that references the axis, or simply have the attributes be independent of the parent. Until then, I have to use a cheat sheet.
its multiple directions at play, since the "cardinal directions" of the parent aren't defined by flex-direction alone. If the writing-mode of a parent block formatting context is set to a vertical mode, then flexbox' "row" will run vertically - which is why flexbox directions are "row" and "column", and can only thought of as "vertical/horizontal" in "horizontal-tb" writing mode.
Further, there's no "bottom to top" mode for horizontal scripts, but vertical modes can have a block axis running either ltr or rtl, affecting the direction of the flex cross axis. Which likely leads to the necessity to also abstract "row-reverse" and "column-reverse" directions for the ordering of items.
now as for distribution of items on either axis (whichever direction it may have), referring rows/columns when might become misleading, and also having to address individual rows (align-content) complicates things. Finding another set of terms for flexbox alone might start to become messy, since display:grid and multicolumn layouts will also require these settings.
I don't know the actual origin of align & justify either, but I have the feeling coming up with better terms might not be that easy
I don’t know if that’s the only reason, so I’m not gonna say it was a bad choice. But at least to me, I’m exactly like you in the sense that I can’t remember which one is which. I would have preferred either better naming that references the axis, or simply have the attributes be independent of the parent. Until then, I have to use a cheat sheet.