That would be an option if you didn't have to turn on Siri for CarPlay. This is really the only reason why I turned it on.
To be correct though, I "use" Siri more often: it is repeatedly triggered when I am on the phone speaking English, even though I have trained it in German and I never use the activation phrase. This unintended activation is really the most annoying part of the whole thing.
I think I can count on the fingers of one hand the number of times I’ve triggered Siri. Dozens of times with Alexa and Google. Goggle’s recognition is better. Know how they got it that way? Guess. Amazon is always lighting up and asking me what I said. I have zero problems if Apple is looking for problems with different pronunciations and/or of the key phrase or how it understands in different acoustics, as long as it is anonymized. How about if you share the problematic stuff, and Apple can figure out what the failure is? No one will know it’s you... Google does.