Money is going to guys who get pressure on the QB, or who remove an opposing receiver in the passing game. Safety is a position where there's a lot of dropoff between the top guys and the median types, the top guys typically have ball skills that can flip the field for you through turnovers but barring that why pay a premium for them?
I suspect Joyner would have made some coin on even this market. Why? Because he can remove a slot receiver. Dude would have gotten paid but the Rams blocked him and took advantage of the market, plain and simple.
Some folks like conspiracy theory and more power to them. I just don't think this league is capable of it. As miniscule as the difference between winning and losing is in the NFL I just don't think you could get all the teams to agree on blackballing a position. To me it's ludicrous but hey to each his own.