Why Integrated Circuit?

What i understand by integrated circuit is connect all the electronic devices placing closer to each other and put it on one substrate.
Why not discrete?
Cost,Speed,Area are the features what today we look at.We need less area,more speed and less cost.
Manufacturing discrete components(single transistor at a time) is costlier than what we can manufacture on single substrate, i.e., printed as a unit by photo lithography.
Cost is less
Placing devices closer to each other improves the performance,devices switch quickly ,as they are smaller and closer.