There is a bias toward backend engineers at the principal engineer level. This leaves frontend engineers heavily disadvantaged when it comes to promotion time.
When someone says they’re a fullstack engineer, what they usually mean is one of two things: 1) They’re a coding bootcamp grad that has minimal experience with Node.js and an emphasis on the frontend. Or, 2) they’re an experienced backend engineer that knows a little bit of HTML and CSS. A truly fullstack software engineer is a rare find.