Because the vast majority here are like minded. They come here and chat about things they agree about. Whether that's an echo-chamber or not is irrelevant: it's a positive experience.
But for you, to be constantly embroiled with dozens of posters at any given time, it just can't be good for your mental health, no matter how much you're about to insinuate the opposite. I would hate to be in a forum of people whose views are in direct conflict with mine. It's just constant negativity.
Unfortunately, while this may be a "political forum" that presents itself as a "for everyone" format, the fact remains that it's 90% conservative. So to see you spend hours a day here fighting with everyone, almost like it's your duty.. it can't be good. Every day, clock in at 9am, constant conflict for hours on end, clock out at 8pm? Maybe never? That's a shit ton of negativity. Same would go if one of us went to a liberal-leaning forum. Uphill battle, you're not swaying anyone, and you're treated like the village idiot. I couldn't do it fot more than a day.