Or I did my research and made an informed decision which to work on. I didn't start working on one then only decide to dislike the other based on sunk cost fallacy. Matrix already existed when I got into doing XMPP stuff, and I looked into both.
I am still aware of both protocols, I still don't like Matrix and think XMPP is "good enough", or at least the best choice. Having an opinion doesn't make me biased against one or the other.
Not being paid for the work on something doesn't imply no bias towards it.
> Having an opinion doesn't make me biased against one or the other.
It might: Confirmation bias