So, repelling blast lets me push an creature 10 ft when i hit it with eldrich blast, however eldrich blast lets me shoot multiple beams, so can i push an creature multiple times with an single casting of eldrich blast, assuming i manage to hit it multiple times?

And why is it that grasp of hadar and lance of leturgy, two rather similar invocations are only able to inflict their effect once on each of your turns, despite repelling blast not having those restrictions even in the newest errata and current print of the players handbook? is pushing people simply an far weaker effect than pulling a creature or reducing their speed, were they worried that an warlock of high level could just reduce an target's speed to 0 and then repeatedly push them? or did they realise they made an mistake when making repelling blast and made shure all future similar invocations were weaker, and then simply forgot to make the same changes to repelling blast?

From what I read, they made a mistake with repelling blast but chose not to fix it because fixing it is too big of a change and it’s been in use as it was originally written for so long. 

ah, thanks