Sorry, but they set their signaling mechanisms so that that signal is worthless. How many people who don't cancel want to signal they are going to be a future customer, as opposed to it being an accident? How many people who do cancel do it to signal they don't want to be a customer, and not because they don't want to be automatically billed? I believe the answer for both is "not many".

I think the companies do it because it benefits them, and because they can.

Are they signaling that they're not going to be a future customer? Or are they just signaling that they want to take positive action if they make the decision to subscribe?

And what about signaling in the other direction? Canceling the trial immediately signals that they have no confidence in the product itself to sell you on it, that the company itself believes that if you use their product for another few days, you still won't want to give them any money for it. If the company has so little confidence in their own product then why would I pay for it?