Along with cycling, I do a lot of walking including a couple of half marathons a year. I avoid walking on most busy MUPs. When the wife and I do walk on one, we go single file and I'm at the back as (1) I'm used to hearing bikes about to pass me and (2) I'd rather be hit than her. One MUP has a 20 mph speed limit; however, a lot of riders think it's a velodrome and go much faster.
However as a cyclist I definitely see the other side also. Many walkers and runners, plus cyclists, are listening to their music with ear buds. I've gotten to the point of not even saying "on your left" as most can't hear me anyway and a lot that do tend to veer to the left when they do hear me. Plus people walking their dogs with the lease all the way out. Or worse, a guy walking their dog while riding a bike!