It wasn't possible in the beginning since, the few new "armies" that joined Afrin op were fighting in Idlib/Hama front.
It's since TR completion of observation point in Idlib front...that things began to speed up (More manpower and equipment in the south front/Jinderes region) That gave TR another point of pressure for YPG, they had to widen their fronts, therefore decrease manpower in other fronts, like the North and West side... And then you get your snowball effect of unbalance of power and things fall faster and faster...
BUT... more the length of the front decrease, more concentrated YPG will be...Things could get slower, when TR/FSA get herself 10-15 km from Afrin city...but since it's mostly flat terrain... intense airstrikes will mostly be used in the outskirt of Afrin...to clean the advance.
And last you get an important Urban Warfare point , that will be Afrin city... that could extend the op for many weeks, if fortified enough and with Civilians inside.
I wonder if TR will open a corridor, when they get to Afrin city, the same used in Aleppo, a safe Road from Afrin to Azaz, that will be under Watch (TR/RU etc...) to give civilians inside, the chance to leave... That could also speed up the Op, by using less "precise" airstrikes to avoid civilians...and therefore could increase the "carpet bombing" effect...
That corridor is also interesting, on the international level... it will show TR goodwill in preserving civilian death and shut up those criticizing them...
We could even get a reverse support effect...if per exemple YPG, doesn't allow citizens to flee on that safe corridor...and therefore use the Civilian shield argument.