Because if all image editing amounted to was adjusting contrast & brightness, we'd all have stopped with Windows Paint.
A photo is the light through the camera lens captured. What it looks like depends on the amount of light that makes it through that lens, and how much of it is captured. Quality depends on the quality of the camera -- the quality of the lens + sensor [or film]. Unless you've got the very rare, perfect photo, editing means making up for imperfections in the camera, and optionally enhancing the image, exaggerating &/or adding features so the scene looks better than real life. Most of the time that means dealing with images where parts of the photo look better than others -- not all light reaches the sensor equally, & not all light is stored equally. TO deal with that we use selections &/or masks -- you select the part(s) of the photo you want to effect, leaving everything else alone.
The selection tools you can use vary with the software you're using, but two things might help make it quicker, easier, & hopefully more accurate. The 1st method is just something I've come to use very often, & that's working on a duplicate layer or a copy of the original file, use the rectangle selection tool, or brush if you prefer, and get rid of most of what you don't want, clearing away the clutter. That can make it less work if your doing any sort of color selection, e.g. the magic wand tool, & helps you to focus just where you need to focus. The idea is to remove everything you don't want, making it fairly easy to select just what you do want -- the selection or mask in this case is a container holding what you want to keep, so if you get rid of everything else, so your selection has a white background, you just select that background then invert your selection. If necessary, say you're working on a copy of the original, then you can save the mask to re-use. If your software won't let you save a mask, fill the selection with black & have the rest of the image white, or vice versa, then copy/paste a copy to an enlarged canvas with the photo you're working on -- then *if needed* make a new selection based on the black object you pasted, & move the selection where you want.
The new idea I picked up this week was to distort the image to make selecting something easier. Some software will let you make changes you can later reverse, &/or alter a duplicate layer -- if not, work on a duplicate file & re-use the selection as above. Use contrast or darken or change color hues etc. to make something really stand out, regardless how terrible it makes your photo look, since all you're after right now is that selection or mask.