Not the first time this issue is raised...
This is a uniquely S'porean issue, because other parts of the
world recognise that having people stand on both sides of the
escalator clears the crowd faster.
Simply speaking, it boils down to the kiasu attitude of people
who can't bear to miss the train, can't stand walking behind others
etc etc.
No, actually this wasn't an issue because the status quo last
time was people just stood on both sides of the
escalator.
If someone wanted to chase the train or was in a hurry, then too
bad, they just had to wait or try the stairs. This was the
norm - if they missed the train, they would not kpkb at all the
passengers in front of them.
Somehow, some scholar decided that to "improve" speed and
efficiency, they decided to come up with the "stand on the left
side unless overtaking " rule.
This rule now forces people to walk up the escalators if they
happen to be on the right.
And since the majority wants to stand left, most passengers tend
to all shift towards that direction thereby causing a small clog at
the base of the escalator.
Speed and efficiency is actually decreased.
Except maybe for the few persons who genuinely needed to move
fast. 
