That's because pink is a feminine color. What don't you understand? And football is a tough, macho, masculine sport.(Well, it was before Goodell took over) Why do you think that anyone with that opinion has some deep underlying issues regarding their own masculinity?
When was the last time you say a bridesmade where hunter green, or navy blue, or black? Would it make them less of a woman? No, but it would look pretty tacky.
The NFL could raise just as much awareness with a big pink ribbon on the field, or a logo on the TV screen, or in any of the relentless commercial breaks. Players wearing pink worked okay at first, now it is just cliche.