As someone who does both Hd 2D and pixelart I can say that I don't think either is easier.
They both have completely different challenges.
And I'm not sure that comparison image really gets the point across, if you were to recreate the hi-res image in pixelart it would be a LOT more difficult than just drawing it straight. Recreating the blocks in full res wouldn't be that difficult I can't imagine.
If you can draw full res 2D then I've found that the challenges of pixelart are kind of refreshing. When you draw something straight you just draw it, thats really the only challenge, being good enough to get it right. With pixels the restrictions of space become an all new challenge, one that I really enjoy tackling.
I'm sure other artists are the same. And there absolutely is the nostalgia aspect as well, I love the idea of making games like the ones I grew up playing.