Reason why 'block-align' was never introduced?

Hi,

I was just facing the problem of centering a block element within a block
element (namely, the infamous table centering in a column). I browsed the
archives - though admittedly not thoroughly - and found the solution to
be { margin-left: auto; margin-right: auto; }. The articles were from
1997 and 1998.

Now, I am simply curiuous what the - probably historical - reason was to
not introduce a 'block-align: left | center | right' property (probably
as a convenient, easily understood and remembered shorthand for the
above, current solution) into CSS.

Thanks for sharing,
Christian