Maturity really isn't the same as age: plenty of legally adult people (many already so for decades) around who are anything but mature individuals.

That said, as others here I think the absence of the subtle pressures derived from commercialization and profit-seeking make most of the difference.

Also, I've been thinking about the possibiility that both those already in Lemmy before and the Reddit refugees who came in recently, are at the most principled end of the spectrum compared with those still in Reddit (whose principles on the subject of ultra-authoritarian top-down imposition as done in Reddit clearly aren't strong enough to make them try something else), possibly also more confortable with change. This might make the crowd here at the moment a self-selected bunch leaning significantly more towards a certain psychological profile than the average which in turn (or so is my theory) affects the dominant tone of discussions here.