Any empirical evidence to show cops are retiring, and replacements can't be hired quickly enough because of Black Lives Matter? It seems like Fox has a narrative they want to push so they sought opinions, some of them anonymous for inexplicable reasons, and ignored all other possibilities. I can think of a big reason recruitment may be down. The economy is improving, and being a police officer is a very tough job. Start with the hours. They suck. You can work all hours of the day, and all days of the week. You can be sitting in your car on Christmas Eve waiting for a call to break up a domestic disturbance instead of being in your house with your family. I've said it many times on this board that it's a tragedy that our police officers are now front line mental health workers. That stuff wears on you.
Throw in a consistent effort to demonize public workers by certain politicians (Cough, Scott Walker… Cough, Bruce Rauner), as parasites who don't earn their benefits and pensions and I can see police officers feeling under appreciated.