sharpness - Why do images look sharp on my camera's LCD, but not tack sharp on my laptop?

I am using a Sigma 18-35mm f1.8 Art lens on a Nikon D7100. On appropriate settings, I see sharp images after pressing the zoom button once, but not before doing that. When I review them on a laptop, though, I can't find images that are as tack sharp as they appear as reviewed on LCD of camera, after pressing zoom.

There is no unnecessary mistakes in garden pictures in shade, with sweet spot, image size comes to 20 MB approx, image setting Raw or Large Fine.... Sometimes I get better image with Nikon 18-140mm.... I am worried but can't find the right solution.