Voice to text and biometrics are noisy sources, so a big part of the problem is dealing with that noise.
Typing is not a noisy source. It should be reliable and deterministic.
Protecting an agent from fairly obvious attacks should also be deterministic.
Typing is absolutely a noisy source.
The fundamental issue is, that "we" somehow decided it would be a good idea to throw all the fundamental ideas of computing (determinism, context, separation between data and execution,...) away and try to solve the issues by running a probabilistic/stochastic word generator on top of deterministic circuits instead at 10 magnitude worse efficiency.