What gives you confidence that they aren't? I have confidence my VPN doesn't sell my traffic not because I implicitly trust what they say, but because if they had logs the courts would have found them when trying to seize data themselves. What makes you trust your ISP so much? Faith in the human goodness of businesses to look out for the best interests of their customers, even if it means passing up an opportunity to make a larger profit? Faith in their words, or faith in toothless privacy laws that have been violated time and time again?
"What gives you confidence that they aren't?"
You're entitled to your conspiracy theories and paranoia of course, but it's not an argument.