I think its because we, as musicians, know exactly what we're playing and don't necessarily realize the complexity of what we're doing.. so that, when we hear it back, its like "Whoa! I played THAT?".. Possibly, anyways.. but, I know what you're talking about..
I have a studio set up at the house.. I use Presonus Studio One and and multiple gizmos to help with recording: a 4 channel interface that you need to plug your stuff into to get it into the computer (Studio One is on the Mac) and another gizmo that allows me physical mixing capabilities so I don't hafta try to drag faders and knobs and stuff with the mouse on the computer - it actually gives me real faders and knobs.. and another gizmo that has pads that I can physically hit in order to trigger stuff like drum sounds or piano etc.. I have TONS of plugins for effects and mixdown stuff and sounds and synthesizers etc..
Its fun, yet amazingly complicated to get good a good mix.. I've decided I'll never be a good sound engineer.. I KNOW the sound I want - just not 100% sure how to achieve it.. For anyone still reading that doesn't know a lot about sound engineering, it IS rocket science.. its AMAZINGLY complicated.. I've decided that I'll use my setup to create the "roadmap" of what I wanna actually lay down in a real studio.. and pay somebody to get the sound I really want.. if I don't, I'll be messing with it for decades.. and I already have been... sigh..
Friendship is like peeing your pants.. Everybody can see it, but only you can feel the warmth..