I’d ask why self-interest needs to be manifested in overtly economic terms.
If you define self-interest broadly enough, then the statement “people pursue their self-interest” becomes irrefutable. And if you cannot refute it, then it is just an empty tautology.
I would much prefer to work with refutable claims than with empty tautologies.
So I continue to treat public choice theory as saying that people pursue economic gain in the political process. With that definition, public choice theory is often wrong, but at least it can be usefully right.