The problem might not be with mindfulness, but with our self-centered culture, which causes this secularized mindfulness to be a snake oil with a few personal benefits at best. It's more of a self-discipline or concentration tool when you strip it from it's culture, which used to involve ethics as I understand.
The original purpose of vipassana (mindfulness meditation) is to realize that selves don’t exist and disconnect you from your emotions, so you’re ready to leave the world behind and do monk stuff. The fact that it works for secular mindfulness is surprising and doesn’t really have any theory behind it.
It doesn’t involve ethics though. Buddhism didn’t come with those; they borrowed standard Western ones as part of a marketing campaign to make you think the Dalai Lama is just the most ethical guy ever.
