> Despite the overarching issues here, what culpability is there when these public safety services who build reliance on these private companies don't do due diligence on what they use?

Are you assuming it's possible?

First, if they're a monopoly, your "due diligence" is "Yep, we need a service and they're the only ones who provide it. We build our own using money we'll never have or we go with them."

Second, cell phone companies are known for lying. Just outright lying. (My proof: If a service is limited, calling it unlimited is a lie.) How can you do due diligence when the party you do it with is lying to you?