Uh, care to explain? I have several colleagues that stopped submitting to journals once they reached full professor. They only submit papers from their students for the benefit of their careers. First-author papers, not so much.
To be clear, the colleagues I am referring to mostly work in math phys. They are sole author papers, but I refer to them as first author, since that is the language I am now accustomed to.
And no, the culture in maths vs. theoretical stats is not really that different at the end of the day, and the latter is most assuredly like other STEM fields. I still collaborate on pure math papers (geometric analysis and PDEs mostly) from time to time, and it isn't really a different head space. My name is typically later in the alphabet, so I never even think about the alphabetical ordering.