They also address that in their response. It stems from the fact that they use memory-managed programming environments, so they don't have that level of control over memory.
That's a pretty extraordinary claim, considering that securing native code is highly nontrivial and increases the attack surface of an application significantly.
The 1password devs specifically say that the Windows team has been playing around with Rust. So they at least seem to be looking into it and treating it as a real possibility.
I don't imagine anything will come from it for a while however.
