I have 6, not including my serger. One is a treadle Singer that I do not use and is willed to my eldest daughter. (It was my first machine that I bought for $16 when I was 16 years old.) My Janome 11000 is upstairs and is the one I use most of the time. Two of my downstairs ones are a New Home (computerized & a real workhorse) and a very basic lightweight Pfaff. I use them both occasionally. The answer to your question, "Why?" is: I needed to upgrade to get features I wanted. I upgraded twice over the last 30 years and, since all my machines work well, it would be foolish to trade them in ... I could never get what they are worth on a trade-in. Machine #5 is the newest ... a Janome 1600DPX bought & set up strictly for quilting. #6 is one my son brought here ... it is old and in a small cabinet. The UK manufacturer is still in business, but I cannot get any e-mail response from them; this machine is missing the bobbin case. The small sturdy cabinet serves as a "table" in my sewing room and the space underneath is is perfect sized space for GO cutter dies/storage rack.
Although I still look at the new, high-end machines (on-line), their specifications & features, I'm currently satisfied with what I have and have no space for more.