This part from the Cosmopolitan link seems to explain it
"People go to the bathroom while they're running — why should bleeding freely be any different?"
" It's more about owning your own comfort level and being confident in your own skin to do what you need to do to accomplish something. Really making it about yourself instead of about other people. For me, it was a bit of a metaphor. I was like, Running a marathon is a very, very big stretch for me. I need to do whatever it takes to get myself to the end of that line. We were running for a greater cause, we were running for breast cancer. When you have that much support, you want to do a good job. That was really part of it — I'm with two of the best, most important women in my life. They stayed with me the whole time. I just wanted it to not matter. But it does matter in our society, right? If it didn't, everyone would be bleeding freely all the time, but instead we have to cover it up."
Surely we have to cover it up? She also says that the reason she decided to bleed freely during the race was because she was scared at what a tampon would do to her while running. Her friend had run a marathon expecting to begin her period while running and had tucked a tampon into her bra. The tampon chafed the skin and left a scar which she didn't want to happen to her if she used a tampon inside. Lots of misconceptions maybe about her reason for running tampon-free.
Taz x