The answer to your question is simple. Scaling random items and random loot is easy to implement. Set scaling parameters, throw in RNG's and *puff* you have taken care of designing gear throughout the whole game problem.

On the other hand, going over the game itself and placing specific unique loot requires a lot of thought and work.

I do not like this lazy approach either, this in not a hack and slash rpg. Sure, you can throw in some random items at vendors and loots, AFTER you place carefully planned items throughout the world, and do it in a waya diverse party of 4 with diverse skillsets can benefit from.