When some guy's get started in the hobby they don't know if they will stay or not and don't want to spend the time it would take to build, they just want to get something in the air in a hurry.

Then there's the pain of crashing your first BUILT plane, all those hours of gluing, cutting, covering and closing those #11 blade cuts on your fingers with CA...

I don't like to build, I do like to fly so I do nothing but ARF's and OPP's.. (other peoples planes)
When I crack one up enough to where it needs "major fixin" I'll strip all the gear out of it and give it away and pull another one out from under my bench and go da work.

After a newbee has a few ARF's under his belt he will start to do what comes natural... MODIFY