Last weekend (in mid-September) I took some wide-angle (24 mm APS-C) photos of a landscape in my vicinity. Despite good illumination (the day was quite sunny), a not-too-long exposure time (1/40"), and a medium aperture (f/8), most pictures look somehow unsharp:
I've already encountered this issue when photographing landscapes in summer with my EOS 70D. What is the cause? Is this maybe an autofocus malfunction? Here is the link to the original pics: Unsharp landscape photos
The problem on these photos seems to be focus, not camera shake or motion blur. You didn't focus on anything visible on the photos, but at a closer distance.
Why this happened, is a question not easy to diagnose if we don't know what you did. It is possible you didn't autofocus at all, or that you picked a wrong autofocus point, or that the autofocus was for some reason confused by the scene.
What I would do in your situation is take some similar photos of landscapes (i.e. a long focusing distance) with the same camera/lens combination and see whether I get any at all that are properly focused. Then try a different lens or maybe even a different camera.
1/40 second is a pretty slow shutter speed for sun-lit pictures.
This is suggestive that you are using a very small aperture, like f/22, which will give you a soft image due to diffraction. On an APS-C sized sensor, f/13 is about the smallest aperture you can use for reasonable sharpness. As a rule of thumb for inexpensive to mid-priced lenses, landscape should use an aperture around f/8. This is a sweet spot for many f/4 lenses and gives you a reasonable depth of field.
Also, hand-holding a camera at 1/40 seconds with a 24mm lens is on the edge of sanity for a person experienced at shooting slow shutter speeds unless you have image stabilization.
You could also be focusing on the wrong thing, perhaps something closer than the scenery.
[Edit]
In regards to the comments why I believe the shutter speed forced the OP to use a small aperture:
Going by the sunny-16 rule which states on a sunny day the shutter speed is the reciprocal of ISO when using an aperture of f/16.
At f/16 and a shutter speed of 1/40 seconds gives an ISO of 40 (going by the sunny-16 rule).
The difference between f/16 and f/8 (as claimed by the OP) is 2-stops.
Thus, the ISO sensitivity on the camera would need to be 10 as Euri points out in the comments, around 3.3-stops off. The 70D minimum ISO is 100.
Perhaps the OP meant to say the shutter speed was 1/400 seconds. Without EXIF data, it's hard to make a reasonable guess as to why the image looks soft.
They look to be focused wrongly, or the lens is soft. I would try a studio test of the lens from a tripod and 2-second delay release, shooting a printed page of high-contrast text to eliminate the lens as an issue. The lens will never be sharper than the image in such a test.
To improve these kind of landscapes, consider using spot focusing mode instead of a scene or evaluative mode. Aim the focus spot at something about 2/3rd of the way "back" to the furthest portion of detail, like the opposite shore of the 2nd photo, and hold the shutter halfway. Then "drag" the viewfinder to frame the shot as you please whilst holding the shutter halfway to lock in that focal distance. That should place the most amount of things you care about in the most focus, including the infinity-distance clouds, which humans expect to appear tack-sharp.
Letting the foreground go a bit soft usually enhances the dimensionality and realism of outdoor scenes, so don't feel like you need to drop down to f8 to perfectly capture the whole range of distance like some tiny aperture smart phone would; those don't tend to look as good/pro/natural/realistic anyway.
Lastly, those images are not all that soft. You won't get a 16x20 from them, but they can easily be sharpened to acceptability on a screen or publication or a typical framed print.
