Why do we throw our fly towards the middle of the lake when we fish from the bank, but throw the fly towards the bank when we fish from a boat?

Makes you feel better buying a boat.

I grew up on a boat but bank fish places that you can't take a boat. I enjoy walking more then floating and I can cast for distance. Same places is if I had a boat.

Because the fish are between the bank and the boat.

I guess I've always looked at it that fly fisherman either fish out of a boat (or some type of floating craft) or wade fish, in which case they are usually casting parallel to the bank. I don't usually see fly fisherman fishing from the bank. But I don't fish ponds much either.

I fly fish in lakes from the bank sometimes and I cast parallel to the bank and toward the middle of the lake. I try and fish where the fish are. Here are a few examples from Whitney, Granbury, and Grapevine.

I didn't know this was supposed to be limited to fly fishing. I (and a lot of others) fish this way with baitcast and spinning gear. Although equally guilty of doing it myself, I've often wondered why so many of us fish this way. I know when I'm in a boat I am fishing weed line, pockets, points, etc.

If I’m on a boat, it’s saltwater, and I’m fishing straight down or trolling.

Osbornfishing: What weight fly rod rod were you using when you caught that big catfish and big carp? Those are monster fish!

I use a browning or eagle claw 6/7 wt for almost all of my freshwater fishing.

Can't go wrong with a 6/7 wt outfit.

I think bank to boat deals with the depth drop off between bank and the middle of water. I expect fish to hide where that depth drop off occurs. Fish would wait for food to come from high elevation to the depths no?

I don't. I cast within 10-12 feet of the bank unless I know there's some kind of structure further out that I want to target.