That's a reasonable answer to why the drivers need to be signed in order to be installed. That's not the question. The question is why should the already-installed drivers that you've been trusting all along suddenly stop working.
It needs to exist in an untrusted environment.. it verifies that the driver which has low level access to the computer hasn't been modified by a third party.. MS signed system binaries are the same way; it's a safeguard against malicious entities.
Does that really not sound ridiculous to you? Microsoft needs to be blamed for their certificate validation implementation because people might use it to make their software expire? Instead of just writing code that does so?
