I sometimes see people arguing for people to work in area A, and declaring a conflict of interest that they are personally working on area A.
If they already were working in area A for unrelated reasons, and then they produced these arguments, it seems reasonable to be worried about motivated reasoning.
On the other hand, if because of these arguments they switched to working in area A, this is in some sense a signal of sincerity ("I'm putting my career where my mouth is").
I don't like the norm of declaring your career as a "conflict of interest", because it implies that you are in the former rather than latter category, regardless of which one is actually true. (And the latter is especially common in EA.) However, I don't really have a candidate alternative norm.
I share your feeling towards it... but I also often say that one's "skin in the game" (your latter example) is someone else's "conflict of interest."
I don't think that the listener / reader is usually in a good position to distinguish between your first and your second example; that's enough to justify the practice of disclosing this as a potential "conflict of interest." In addition, by knowing you already work for cause X, I might consider if your case is affected by some kind of cognitive bias.
I'm not objecting to providing the information (I think that is good), I'm objecting to calling it a "conflict of interest".
I'd be much more keen on something like this (source):
For transparency, note that the reports for the latter three rows are all Open Philanthropy analyses, and I am co-CEO of Open Philanthropy.