Because Lemmy is equally an echo chamber, and historically people do not like being reminded of inconvenient truths.
Lemmy is an echo chamber you make yourself tho. There are no algorithms that push certain content to you. Obviously, if you only lurk on shit like hexbear, my condolences, but I don’t feel like Lemmy is an echo chamber, at least much less than reddit was.
Echo chambers are not dependent on having an algorithmic feed. It just matters that the people you talk with and the information you consume, etc, filter out dissenting opinions from what you hold.
Lemmy is still very much an echo chamber simply by virtue of the people who tend to be here. But we can balance that with time spent on other platforms, IRL relationships, etc.