Because it's different than pretty much all other modern software. Nearly all other software you follow you click on things to select them. Shift click or Ctrl click to add to your selection. Once something is selected you can move it. Even here in this browser I'm using the write this comment I can select some text, if I then drag the selection it moves, if I right click, ctrl click a bunch of options appear related to what I selected. The menu options also affect the selection.
Blender is pretty much the only program I use of the 100s I have that doesn't follow this UI pattern so I can't take all the knowledge of the other 100s of apps I use and apply that knowledge to blender. Even limiting to just 3D programs I can figure out Maya, 3DSMax, Cinema 3D, DAZ etc just by doing what I do in all other software. Select stuff and then see what my options are. Blender though doesn't follow these rules. You can't just explore. You absolutely have to read the manual to even just load, select, move, and save. Something I can do in all other software without a manual.
Blender is pretty much the only program I use of the 100s I have that doesn't follow this UI pattern so I can't take all the knowledge of the other 100s of apps I use and apply that knowledge to blender. Even limiting to just 3D programs I can figure out Maya, 3DSMax, Cinema 3D, DAZ etc just by doing what I do in all other software. Select stuff and then see what my options are. Blender though doesn't follow these rules. You can't just explore. You absolutely have to read the manual to even just load, select, move, and save. Something I can do in all other software without a manual.