Why is it so hard to draw with a tablet ?

I've been drawing for years, and I've bought a tablet, (I'm a good drawer, check out my gallery if you want: kaithelonechampion.deviantart.com ) and it seems I can't do shades or draw as good as I usually do, can you give me any tips to make it easier ? Or why is it so hard ?
Update: @aniston do you mean I'm a bad drawer OVERALL ? Or just on the tablet ?
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