>The whole reason I brought this up is because I want to know why you guys write replies this way, and if you always did. I'm intrigued.

These are my ways and reasons:

If the post I'm replying to is short (one or two paragraphs), I leave it all.

If it's longer, and/or I'm only replying to a particular part of it, I leave only enough of the original to indicate what I am replying to.

I find it incredibly annoying to read one-line replies after scrolling down a whole page's worth of original post, and it takes up forum space without adding anything new. I also resist single-line responses inserted every couple of lines throughout an original post, because I find this style difficult to follow, and near-impossible if several people continue it throughout a thread.