The Nikon is processing 20% more data (24 MP vs. 20 MP), and presumably writing out 20% more data. That's part of the difference. The rest of the difference is likely in the size of the buffer.
yes fair , but the nikon d7000 also had a very poor buffer compared to the 60d
70d: 16 raw files ( shoots 22 with fast card before slowdown) (7fps)
d7100 6 raw files (slows down after 5-6, 5fps in 14 bit raw)
60d 16 raw files (5.3 fps)
d7000 10 raw (6fps)
I know the d7000-d7100 is from 16 to 24 mpixel,
but the canon went from 18 to 20 and retained the amount of shots that could be taken
I have always been annoyed by a small buffer since it should be fairly cheap to put more buffer memory in a camera.
When you shoot raw+jpg these numbers off course get worse.
I had it happen a few years ago with a river crossing of lions , where I used a d7000 and shot raw to one card, jpg as backup to the other, with a fairly slow card (45mb/s).
After only a few shots it went down to around 1fps .
Since then I have stopped backing up jpg to the second card slot and looked for a camera with slightly better buffer. I can understand to some people buffer doesn't matter at all , but I think it is also often overlooked when people are out to buy their first DSLR ( with the intention to shoot wildlife sports)