This could be me. I had about 15 UFOs, then a friend gave me another 15... I seem to have a block around actually finishing a quilt, and have spent a lot of time trying to work out why. I go for long periods not doing any sewing because I feel overwhelmed and discouraged - unless I'm starting something new (: Yet when I get going again, I love it and wonder why I don't do it every day.
I decided that the number of UFOs I could see in my sewing room was draining and intimidating me, so I bundled them all up and put them away out of sight. It helped. Now I'm working on one project, with a second coming out if the first comes to a temporary halt because I need to buy something before I can continue.
I gve myself permission not to worry about the UFOs or to think that I "ought" to finish them before starting something new. So occasionally I'll get one of them out and finish it, or I may go for something new -the only rule now is that none of the new projects join the UFOs!
But why do I just stop sewing for long periods? Haven't worked out the answer to that. I'm retired, the time's there if I want it to be, I'm happy when I do sew regularly, but I go weeks and months without doing anything.
We humans are strange creatures!