Because it's new people on here and both artist have evolved or decrease. They both put out new music. They're not the same artist they were 10 years ago. People might not feel the same way they did 5 years ago.
Cosistency in hip hop is very hard to achieve. You got 1 person writing thousands of lines of songs. Thats why most rappers are done after a few years. Elite rappers are those with 3 really good albums and that shit is rare.
Unfortunately, consistency is not respected as much as it should be.
I gotta go with the mighty Mos Def but its close. Their both 50% responsible for the classic Black Star album. They both got 2 classic solo albums(ya im callin RE a solo). But then it changes bc Mos only got a couple other albums and Kweli got a bunch of shit, some good some bad. Mos didnt drop anything wack till Dec 99th.
But when it comes down to whos flat out nicer on the mic, its Mos.