The short and to the point answer is that members used no discretion in quoting. That is, they quote the entire
text of long posts, just to make an answer to only one point of the quoted text.
In other words, the function was abused. Because of that, we have removed the buttons, but the function remains. It has to be manually used.
How do you do that?
Read this thread: How Do I Quote From A Post?
It's up in the "stickies" at the top of the index for this section of TFL.