The difference is they did it for 2014. While many Disney shows and other animation companies used Rap because it was hip in the late 90s/Early 2000s (The Titanic movie with the Rapping dog came out in 2000. So right smack dab in the middle there). So about 1 ½ decades for the animation companies to finally get their mind straight that Rap isn’t hip anymore and only use it sparingly so it doesn’t feel like lame attempts to get with the times.

AKR did it as a funny little reference rather then doing it just because it’s “hip” or “cool”. If they were going for what’s “cool” but often criticized for being overdone in recent times, they’d go with something like Dubstep. Kids now aren’t as familiar with rap as those who grew up to the 90s are. Just like how kids who grew up in the 80s don’t remember too much about Disco that the kids of the 70s remember much more. 

Unless it became a trend in cartoons again somehow. Using Rap in cartoons is about the same as having a character dance to disco for laughs now: It’s partly funny in the first place because it’s old school now.