I'd guess that a given academic isn't going to face much of a career risk for signing a statement also signed by other very prestigious academics, just the opposite. There's no part of very divided US political spectrum that I can see denouncing AI naysayers, unlike the scientists who signed anti-nuclear statements in 1960s or even people warning about global warming now (indeed, I'd guess the statement doesn't mention climate change 'cause it's still a sore point).
Moreover, talking about existential risk involves the assumption the current tech is going to continue to affect more and more fields rather than peaking at some point - this assumption guarantees more funding along with funding for risk.
All that said, I don't necessarily think the scientists involved are insincere. Rather, I would expect they're worried and signed this vague statement because it was something that might get traction. While the companies indeed may be "genuine" in the sense they're vaguely [concerned - edit] and also self-serving - "here's a hard problem it's important to have us wise, smart people in charge of and profiting from"
In interviews, Geoffrey Hinton and Yoshua Bengio certainly expressed serious concerns and even some plausible regret to their life’s work. They did not say anything that can be interpreted as your last sentence suggests at all.
My last sentence currently: "While the companies indeed may be "genuine" in the sense they're vaguely and also self-serving - "here's a hard problem it's important to have us wise, smart people in charge of and profiting from" - IE, I am not referring to the academics there.
I'm going to edit the sentence to fill in some missing words but I don't think this will change the meaning involved.
Moreover, talking about existential risk involves the assumption the current tech is going to continue to affect more and more fields rather than peaking at some point - this assumption guarantees more funding along with funding for risk.
All that said, I don't necessarily think the scientists involved are insincere. Rather, I would expect they're worried and signed this vague statement because it was something that might get traction. While the companies indeed may be "genuine" in the sense they're vaguely [concerned - edit] and also self-serving - "here's a hard problem it's important to have us wise, smart people in charge of and profiting from"