Moving will be made to interrupt spellcasting at a point in time...

[Celtodeno]

A mage casting while running around is the equivalent of someone knitting while jogging.

No wait, much worse.

Someone performing brain surgery while hopping.

Well the problem with this logic is that knitting and performing brain surgery are things that people do in real life, while casting magic is something that is never done in real life. You will never find it written in the journals of science that magic casting is a stationary affair.

Casting while moving or having to stand still while casting is a by-product of code, nothing else. It's a choice made by the developers.