It’s an interesting question indeed.
At the first glance, I know that I could fall under this irrational category.
But there’s additional parameters that could be easily overlooked, in my case for example the fact that sushiswap offers services such as limit orders, that according to their own website go through unaudited code, that’s a red flag.
Other than that I’m also thinking that imminent announcements about V3 could be the reason why this is taking longer than expected.
Which is why I’m a uni holder, which is why I favor Uniswap as a user.
There’s still some irrationality in this (Uniswap fanboyism) but it’s probably a minor component of the choice.
I think a major part of it is also simply awareness: frequent defi users all know sushiswap, sure. Other users, not necessarily. They might know the name, but as long as Uniswap is satisfying enough, why bother spending some time determining if alternatives would justify switching platorms?