While I am sympathetic to the wish for these things to be opt in, there is major issues with relying on such efforts.

Organ Donation in the US for example, is an opt-in scenario. The shortage of organs for transplant would be drastically reduced, albiet not eliminated, if this was instead opt-out.

Most people will never change their defaults of anything in life. While voice interfaces are hardly as important as Organ Donation, if it was opt-in Google would have to contend with a much smaller dataset to train their AI, and the rate of progress would slow down drastically, even if it didn't stop completely.

That's why I'm generally in favor for making this stuff opt-out instead of opt-in. Most people will not care enough to change their settings either way, but thsoe that do would ideally be allowed to do so.

For now, the only options are either participate in helping these things advance and the company that owns them make money or just never use them in the first place.