To me, the saddest thing about "mindfulness" is that it is to existentialism what the Taliban is to statues of Buddha. A very blunt tool for people without enough time or patience to examine reality or actually ask, "why is this thing here? Might it mean something?" This is pop-cultural garbage taken to cult level to overwhelm fragile peoples' minds, without giving them a chance to understand the historical context of their place and time or what reason they might actually have to be going through the things they're going through.
So mindfulness leading to egoism is a foregone conclusion, because it's a degenerated version of existential or Buddhist thought, intentionally turned into trifling horseshit for people who were born, live, and will die without any notion or care of anything that happened before them. And they were already egoists; and having a problem you can't frame in broader terms than your own ability to pay attention to it for a few minutes is having a pretty pathetic problem indeed.