Actually the 19te and the 1stEPI and friends - we march in line and it is often times a better idea than using the infamous and slow snake column. We also use double ranks to allow for quicker movement, in which as the 19te we often times deploy back into single rank to avoid unwanted casualties that ensues when using the double ranks.
They are used, you just don't notice. A lot of the regiments on MM are the new ones, there seems to be a circle of merging and disbandment over a period of time. Some last a few weeks - some a few months, but I think this has an effect on the amount of experience each one gets. And it not uncommon for commanders to worry about keeping people alive rather than honoring the linebattle and its meaning. IE : skirmish charge, spread out and charge, behind the hill peek-a-boo, the list goes on and on.
I would love to see more people playing linebattles for the fun, instead of the highscores!