There are many differences between normal people and rationalists other than level of tribalism. For example, rationalists are disproportionately likely to be LGBT and autistic, and for various reasons LGBT and autistic people are more likely to be depressed. You don't seem to have provided any evidence that level of tribalism is the important factor here.

It seems basically confused to imagine that we start with a bunch of individuals who might choose to get along in liberal society, and then some defect causes them to gratuitously engage in tribalism. Rather, humans are social animals who evolved to function well in groups with a lot of shared local information and norms, and liberal individualism is a comparatively unusual practice built on that substrate. If we want to sustain it outside its historical origins, we need to understand the social technologies necessary to support it.

This also means that it's confused to try to "do tribalism" in a consumerist way, as one in a range of separate, more or less independent things you participate in. The norms of your community - and the vast majority of us are part of the global cosmopolitan liberal community, even the conservatives, neoreactionaries, and other such pseudo-old-fashioned weirdos among us - are how you come to be someone in particular in the first place. Tribal rituals and affiliations that don't get integrated into the fabric of our way of life will die out as they go out of fashion. The others will change us. We should take care to change ourselves for the better.

If you look at the data, it turns out that normal people are considerably happier than rationalists.

Towards what data are you pointing?

I think most rationalists are way more in favor of tribal stuff than you're implying. The Solstice is just one example.

We're not shunning it because it's what normies use, it's just hard to start it from scratch. If you start doing these things, I bet a lot of people would be interested in them.